diff --git a/mypy/typeshed/stdlib/@tests/test_cases/asyncio/check_coroutines.py b/mypy/typeshed/stdlib/@tests/test_cases/asyncio/check_coroutines.py
new file mode 100644
index 000000000000..160bd896469e
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/asyncio/check_coroutines.py
@@ -0,0 +1,25 @@
+from __future__ import annotations
+
+from asyncio import iscoroutinefunction
+from collections.abc import Awaitable, Callable, Coroutine
+from typing import Any
+from typing_extensions import assert_type
+
+
+def test_iscoroutinefunction(
+    x: Callable[[str, int], Coroutine[str, int, bytes]],
+    y: Callable[[str, int], Awaitable[bytes]],
+    z: Callable[[str, int], str | Awaitable[bytes]],
+    xx: object,
+) -> None:
+    if iscoroutinefunction(x):
+        assert_type(x, Callable[[str, int], Coroutine[str, int, bytes]])
+
+    if iscoroutinefunction(y):
+        assert_type(y, Callable[[str, int], Coroutine[Any, Any, bytes]])
+
+    if iscoroutinefunction(z):
+        assert_type(z, Callable[[str, int], Coroutine[Any, Any, Any]])
+
+    if iscoroutinefunction(xx):
+        assert_type(xx, Callable[..., Coroutine[Any, Any, Any]])
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/asyncio/check_gather.py b/mypy/typeshed/stdlib/@tests/test_cases/asyncio/check_gather.py
new file mode 100644
index 000000000000..02a01e39731a
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/asyncio/check_gather.py
@@ -0,0 +1,38 @@
+from __future__ import annotations
+
+import asyncio
+from typing import Awaitable, List, Tuple, Union
+from typing_extensions import assert_type
+
+
+async def coro1() -> int:
+    return 42
+
+
+async def coro2() -> str:
+    return "spam"
+
+
+async def test_gather(awaitable1: Awaitable[int], awaitable2: Awaitable[str]) -> None:
+    a = await asyncio.gather(awaitable1)
+    assert_type(a, Tuple[int])
+
+    b = await asyncio.gather(awaitable1, awaitable2, return_exceptions=True)
+    assert_type(b, Tuple[Union[int, BaseException], Union[str, BaseException]])
+
+    c = await asyncio.gather(awaitable1, awaitable2, awaitable1, awaitable1, awaitable1, awaitable1)
+    assert_type(c, Tuple[int, str, int, int, int, int])
+
+    d = await asyncio.gather(awaitable1, awaitable1, awaitable1, awaitable1, awaitable1, awaitable1, awaitable1)
+    assert_type(d, List[int])
+
+    awaitables_list: list[Awaitable[int]] = [awaitable1]
+    e = await asyncio.gather(*awaitables_list)
+    assert_type(e, List[int])
+
+    # this case isn't reliable between typecheckers, no one would ever call it with no args anyway
+    # f = await asyncio.gather()
+    # assert_type(f, list[Any])
+
+
+asyncio.run(test_gather(coro1(), coro2()))
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/asyncio/check_task.py b/mypy/typeshed/stdlib/@tests/test_cases/asyncio/check_task.py
new file mode 100644
index 000000000000..69bcf8f782aa
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/asyncio/check_task.py
@@ -0,0 +1,28 @@
+from __future__ import annotations
+
+import asyncio
+
+
+class Waiter:
+    def __init__(self) -> None:
+        self.tasks: list[asyncio.Task[object]] = []
+
+    def add(self, t: asyncio.Task[object]) -> None:
+        self.tasks.append(t)
+
+    async def join(self) -> None:
+        await asyncio.wait(self.tasks)
+
+
+async def foo() -> int:
+    return 42
+
+
+async def main() -> None:
+    # asyncio.Task is covariant in its type argument, which is unusual since its parent class
+    # asyncio.Future is invariant in its type argument. This is only sound because asyncio.Task
+    # is not actually Liskov substitutable for asyncio.Future: it does not implement set_result.
+    w = Waiter()
+    t: asyncio.Task[int] = asyncio.create_task(foo())
+    w.add(t)
+    await w.join()
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_dict-py39.py b/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_dict-py39.py
new file mode 100644
index 000000000000..d707cfed222e
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_dict-py39.py
@@ -0,0 +1,67 @@
+"""
+Tests for `dict.__(r)or__`.
+
+`dict.__or__` and `dict.__ror__` were only added in py39,
+hence why these are in a separate file to the other test cases for `dict`.
+"""
+
+from __future__ import annotations
+
+import os
+import sys
+from typing import Mapping, TypeVar, Union
+from typing_extensions import Self, assert_type
+
+_KT = TypeVar("_KT")
+_VT = TypeVar("_VT")
+
+if sys.version_info >= (3, 9):
+
+    class CustomDictSubclass(dict[_KT, _VT]):
+        pass
+
+    class CustomMappingWithDunderOr(Mapping[_KT, _VT]):
+        def __or__(self, other: Mapping[_KT, _VT]) -> dict[_KT, _VT]:
+            return {}
+
+        def __ror__(self, other: Mapping[_KT, _VT]) -> dict[_KT, _VT]:
+            return {}
+
+        def __ior__(self, other: Mapping[_KT, _VT]) -> Self:
+            return self
+
+    def test_dict_dot_or(
+        a: dict[int, int],
+        b: CustomDictSubclass[int, int],
+        c: dict[str, str],
+        d: Mapping[int, int],
+        e: CustomMappingWithDunderOr[str, str],
+    ) -> None:
+        # dict.__(r)or__ always returns a dict, even if called on a subclass of dict:
+        assert_type(a | b, dict[int, int])
+        assert_type(b | a, dict[int, int])
+
+        assert_type(a | c, dict[Union[int, str], Union[int, str]])
+
+        # arbitrary mappings are not accepted by `dict.__or__`;
+        # it has to be a subclass of `dict`
+        a | d  # type: ignore
+
+        # but Mappings such as `os._Environ` or `CustomMappingWithDunderOr`,
+        # which define `__ror__` methods that accept `dict`, are fine:
+        assert_type(a | os.environ, dict[Union[str, int], Union[str, int]])
+        assert_type(os.environ | a, dict[Union[str, int], Union[str, int]])
+
+        assert_type(c | os.environ, dict[str, str])
+        assert_type(c | e, dict[str, str])
+
+        assert_type(os.environ | c, dict[str, str])
+        assert_type(e | c, dict[str, str])
+
+        e |= c
+        e |= a  # type: ignore
+
+        # TODO: this test passes mypy, but fails pyright for some reason:
+        # c |= e
+
+        c |= a  # type: ignore
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_dict.py b/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_dict.py
new file mode 100644
index 000000000000..aa920d045cbc
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_dict.py
@@ -0,0 +1,58 @@
+from __future__ import annotations
+
+from typing import Dict, Generic, Iterable, TypeVar
+from typing_extensions import assert_type
+
+# These do follow `__init__` overloads order:
+# mypy and pyright have different opinions about this one:
+# mypy raises: 'Need type annotation for "bad"'
+# pyright is fine with it.
+# bad = dict()
+good: dict[str, str] = dict()
+assert_type(good, Dict[str, str])
+
+assert_type(dict(arg=1), Dict[str, int])
+
+_KT = TypeVar("_KT")
+_VT = TypeVar("_VT")
+
+
+class KeysAndGetItem(Generic[_KT, _VT]):
+    data: dict[_KT, _VT]
+
+    def __init__(self, data: dict[_KT, _VT]) -> None:
+        self.data = data
+
+    def keys(self) -> Iterable[_KT]:
+        return self.data.keys()
+
+    def __getitem__(self, __k: _KT) -> _VT:
+        return self.data[__k]
+
+
+kt1: KeysAndGetItem[int, str] = KeysAndGetItem({0: ""})
+assert_type(dict(kt1), Dict[int, str])
+dict(kt1, arg="a")  # type: ignore
+
+kt2: KeysAndGetItem[str, int] = KeysAndGetItem({"": 0})
+assert_type(dict(kt2, arg=1), Dict[str, int])
+
+
+def test_iterable_tuple_overload(x: Iterable[tuple[int, str]]) -> dict[int, str]:
+    return dict(x)
+
+
+i1: Iterable[tuple[int, str]] = [(1, "a"), (2, "b")]
+test_iterable_tuple_overload(i1)
+dict(i1, arg="a")  # type: ignore
+
+i2: Iterable[tuple[str, int]] = [("a", 1), ("b", 2)]
+assert_type(dict(i2, arg=1), Dict[str, int])
+
+i3: Iterable[str] = ["a.b"]
+i4: Iterable[bytes] = [b"a.b"]
+assert_type(dict(string.split(".") for string in i3), Dict[str, str])
+assert_type(dict(string.split(b".") for string in i4), Dict[bytes, bytes])
+
+dict(["foo", "bar", "baz"])  # type: ignore
+dict([b"foo", b"bar", b"baz"])  # type: ignore
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_exception_group-py311.py b/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_exception_group-py311.py
new file mode 100644
index 000000000000..e53cd12288a4
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_exception_group-py311.py
@@ -0,0 +1,323 @@
+from __future__ import annotations
+
+import sys
+from typing import TypeVar
+from typing_extensions import assert_type
+
+if sys.version_info >= (3, 11):
+    # This can be removed later, but right now Flake8 does not know
+    # about these two classes:
+    from builtins import BaseExceptionGroup, ExceptionGroup
+
+    # BaseExceptionGroup
+    # ==================
+    # `BaseExceptionGroup` can work with `BaseException`:
+    beg = BaseExceptionGroup("x", [SystemExit(), SystemExit()])
+    assert_type(beg, BaseExceptionGroup[SystemExit])
+    assert_type(beg.exceptions, tuple[SystemExit | BaseExceptionGroup[SystemExit], ...])
+
+    # Covariance works:
+    _beg1: BaseExceptionGroup[BaseException] = beg
+
+    # `BaseExceptionGroup` can work with `Exception`:
+    beg2 = BaseExceptionGroup("x", [ValueError()])
+    # FIXME: this is not right, runtime returns `ExceptionGroup` instance instead,
+    # but I am unable to represent this with types right now.
+    assert_type(beg2, BaseExceptionGroup[ValueError])
+
+    # .subgroup()
+    # -----------
+
+    assert_type(beg.subgroup(KeyboardInterrupt), BaseExceptionGroup[KeyboardInterrupt] | None)
+    assert_type(beg.subgroup((KeyboardInterrupt,)), BaseExceptionGroup[KeyboardInterrupt] | None)
+
+    def is_base_exc(exc: BaseException) -> bool:
+        return isinstance(exc, BaseException)
+
+    def is_specific(exc: SystemExit | BaseExceptionGroup[SystemExit]) -> bool:
+        return isinstance(exc, SystemExit)
+
+    # This one does not have `BaseExceptionGroup` part,
+    # this is why we treat as an error.
+    def is_system_exit(exc: SystemExit) -> bool:
+        return isinstance(exc, SystemExit)
+
+    def unrelated_subgroup(exc: KeyboardInterrupt) -> bool:
+        return False
+
+    assert_type(beg.subgroup(is_base_exc), BaseExceptionGroup[SystemExit] | None)
+    assert_type(beg.subgroup(is_specific), BaseExceptionGroup[SystemExit] | None)
+    beg.subgroup(is_system_exit)  # type: ignore
+    beg.subgroup(unrelated_subgroup)  # type: ignore
+
+    # `Exception`` subgroup returns `ExceptionGroup`:
+    assert_type(beg.subgroup(ValueError), ExceptionGroup[ValueError] | None)
+    assert_type(beg.subgroup((ValueError,)), ExceptionGroup[ValueError] | None)
+
+    # Callable are harder, we don't support cast to `ExceptionGroup` here.
+    # Because callables might return `True` the first time. And `BaseExceptionGroup`
+    # will stick, no matter what arguments are.
+
+    def is_exception(exc: Exception) -> bool:
+        return isinstance(exc, Exception)
+
+    def is_exception_or_beg(exc: Exception | BaseExceptionGroup[SystemExit]) -> bool:
+        return isinstance(exc, Exception)
+
+    # This is an error because of the `Exception` argument type,
+    # while `SystemExit` is needed instead.
+    beg.subgroup(is_exception_or_beg)  # type: ignore
+
+    # This is an error, because `BaseExceptionGroup` is not an `Exception`
+    # subclass. It is required.
+    beg.subgroup(is_exception)  # type: ignore
+
+    # .split()
+    # --------
+
+    assert_type(
+        beg.split(KeyboardInterrupt), tuple[BaseExceptionGroup[KeyboardInterrupt] | None, BaseExceptionGroup[SystemExit] | None]
+    )
+    assert_type(
+        beg.split((KeyboardInterrupt,)),
+        tuple[BaseExceptionGroup[KeyboardInterrupt] | None, BaseExceptionGroup[SystemExit] | None],
+    )
+    assert_type(
+        beg.split(ValueError),  # there are no `ValueError` items in there, but anyway
+        tuple[ExceptionGroup[ValueError] | None, BaseExceptionGroup[SystemExit] | None],
+    )
+
+    excs_to_split: list[ValueError | KeyError | SystemExit] = [ValueError(), KeyError(), SystemExit()]
+    to_split = BaseExceptionGroup("x", excs_to_split)
+    assert_type(to_split, BaseExceptionGroup[ValueError | KeyError | SystemExit])
+
+    # Ideally the first part should be `ExceptionGroup[ValueError]` (done)
+    # and the second part should be `BaseExceptionGroup[KeyError | SystemExit]`,
+    # but we cannot subtract type from a union.
+    # We also cannot change `BaseExceptionGroup` to `ExceptionGroup` even if needed
+    # in the second part here because of that.
+    assert_type(
+        to_split.split(ValueError),
+        tuple[ExceptionGroup[ValueError] | None, BaseExceptionGroup[ValueError | KeyError | SystemExit] | None],
+    )
+
+    def split_callable1(exc: ValueError | KeyError | SystemExit | BaseExceptionGroup[ValueError | KeyError | SystemExit]) -> bool:
+        return True
+
+    assert_type(
+        to_split.split(split_callable1),  # Concrete type is ok
+        tuple[
+            BaseExceptionGroup[ValueError | KeyError | SystemExit] | None,
+            BaseExceptionGroup[ValueError | KeyError | SystemExit] | None,
+        ],
+    )
+    assert_type(
+        to_split.split(is_base_exc),  # Base class is ok
+        tuple[
+            BaseExceptionGroup[ValueError | KeyError | SystemExit] | None,
+            BaseExceptionGroup[ValueError | KeyError | SystemExit] | None,
+        ],
+    )
+    # `Exception` cannot be used: `BaseExceptionGroup` is not a subtype of it.
+    to_split.split(is_exception)  # type: ignore
+
+    # .derive()
+    # ---------
+
+    assert_type(beg.derive([ValueError()]), ExceptionGroup[ValueError])
+    assert_type(beg.derive([KeyboardInterrupt()]), BaseExceptionGroup[KeyboardInterrupt])
+
+    # ExceptionGroup
+    # ==============
+
+    # `ExceptionGroup` can work with `Exception`:
+    excs: list[ValueError | KeyError] = [ValueError(), KeyError()]
+    eg = ExceptionGroup("x", excs)
+    assert_type(eg, ExceptionGroup[ValueError | KeyError])
+    assert_type(eg.exceptions, tuple[ValueError | KeyError | ExceptionGroup[ValueError | KeyError], ...])
+
+    # Covariance works:
+    _eg1: ExceptionGroup[Exception] = eg
+
+    # `ExceptionGroup` cannot work with `BaseException`:
+    ExceptionGroup("x", [SystemExit()])  # type: ignore
+
+    # .subgroup()
+    # -----------
+
+    # Our decision is to ban cases like::
+    #
+    #   >>> eg = ExceptionGroup('x', [ValueError()])
+    #   >>> eg.subgroup(BaseException)
+    #   ExceptionGroup('e', [ValueError()])
+    #
+    # are possible in runtime.
+    # We do it because, it does not make sense for all other base exception types.
+    # Supporting just `BaseException` looks like an overkill.
+    eg.subgroup(BaseException)  # type: ignore
+    eg.subgroup((KeyboardInterrupt, SystemExit))  # type: ignore
+
+    assert_type(eg.subgroup(Exception), ExceptionGroup[Exception] | None)
+    assert_type(eg.subgroup(ValueError), ExceptionGroup[ValueError] | None)
+    assert_type(eg.subgroup((ValueError,)), ExceptionGroup[ValueError] | None)
+
+    def subgroup_eg1(exc: ValueError | KeyError | ExceptionGroup[ValueError | KeyError]) -> bool:
+        return True
+
+    def subgroup_eg2(exc: ValueError | KeyError) -> bool:
+        return True
+
+    assert_type(eg.subgroup(subgroup_eg1), ExceptionGroup[ValueError | KeyError] | None)
+    assert_type(eg.subgroup(is_exception), ExceptionGroup[ValueError | KeyError] | None)
+    assert_type(eg.subgroup(is_base_exc), ExceptionGroup[ValueError | KeyError] | None)
+    assert_type(eg.subgroup(is_base_exc), ExceptionGroup[ValueError | KeyError] | None)
+
+    # Does not have `ExceptionGroup` part:
+    eg.subgroup(subgroup_eg2)  # type: ignore
+
+    # .split()
+    # --------
+
+    assert_type(eg.split(TypeError), tuple[ExceptionGroup[TypeError] | None, ExceptionGroup[ValueError | KeyError] | None])
+    assert_type(eg.split((TypeError,)), tuple[ExceptionGroup[TypeError] | None, ExceptionGroup[ValueError | KeyError] | None])
+    assert_type(
+        eg.split(is_exception), tuple[ExceptionGroup[ValueError | KeyError] | None, ExceptionGroup[ValueError | KeyError] | None]
+    )
+    assert_type(
+        eg.split(is_base_exc),
+        # is not converted, because `ExceptionGroup` cannot have
+        # direct `BaseException` subclasses inside.
+        tuple[ExceptionGroup[ValueError | KeyError] | None, ExceptionGroup[ValueError | KeyError] | None],
+    )
+
+    # It does not include `ExceptionGroup` itself, so it will fail:
+    def value_or_key_error(exc: ValueError | KeyError) -> bool:
+        return isinstance(exc, (ValueError, KeyError))
+
+    eg.split(value_or_key_error)  # type: ignore
+
+    # `ExceptionGroup` cannot have direct `BaseException` subclasses inside.
+    eg.split(BaseException)  # type: ignore
+    eg.split((SystemExit, GeneratorExit))  # type: ignore
+
+    # .derive()
+    # ---------
+
+    assert_type(eg.derive([ValueError()]), ExceptionGroup[ValueError])
+    assert_type(eg.derive([KeyboardInterrupt()]), BaseExceptionGroup[KeyboardInterrupt])
+
+    # BaseExceptionGroup Custom Subclass
+    # ==================================
+    # In some cases `Self` type can be preserved in runtime,
+    # but it is impossible to express. That's why we always fallback to
+    # `BaseExceptionGroup` and `ExceptionGroup`.
+
+    _BE = TypeVar("_BE", bound=BaseException)
+
+    class CustomBaseGroup(BaseExceptionGroup[_BE]): ...
+
+    cb1 = CustomBaseGroup("x", [SystemExit()])
+    assert_type(cb1, CustomBaseGroup[SystemExit])
+    cb2 = CustomBaseGroup("x", [ValueError()])
+    assert_type(cb2, CustomBaseGroup[ValueError])
+
+    # .subgroup()
+    # -----------
+
+    assert_type(cb1.subgroup(KeyboardInterrupt), BaseExceptionGroup[KeyboardInterrupt] | None)
+    assert_type(cb2.subgroup((KeyboardInterrupt,)), BaseExceptionGroup[KeyboardInterrupt] | None)
+
+    assert_type(cb1.subgroup(ValueError), ExceptionGroup[ValueError] | None)
+    assert_type(cb2.subgroup((KeyError,)), ExceptionGroup[KeyError] | None)
+
+    def cb_subgroup1(exc: SystemExit | CustomBaseGroup[SystemExit]) -> bool:
+        return True
+
+    def cb_subgroup2(exc: ValueError | CustomBaseGroup[ValueError]) -> bool:
+        return True
+
+    assert_type(cb1.subgroup(cb_subgroup1), BaseExceptionGroup[SystemExit] | None)
+    assert_type(cb2.subgroup(cb_subgroup2), BaseExceptionGroup[ValueError] | None)
+    cb1.subgroup(cb_subgroup2)  # type: ignore
+    cb2.subgroup(cb_subgroup1)  # type: ignore
+
+    # .split()
+    # --------
+
+    assert_type(
+        cb1.split(KeyboardInterrupt), tuple[BaseExceptionGroup[KeyboardInterrupt] | None, BaseExceptionGroup[SystemExit] | None]
+    )
+    assert_type(cb1.split(TypeError), tuple[ExceptionGroup[TypeError] | None, BaseExceptionGroup[SystemExit] | None])
+    assert_type(cb2.split((TypeError,)), tuple[ExceptionGroup[TypeError] | None, BaseExceptionGroup[ValueError] | None])
+
+    def cb_split1(exc: SystemExit | CustomBaseGroup[SystemExit]) -> bool:
+        return True
+
+    def cb_split2(exc: ValueError | CustomBaseGroup[ValueError]) -> bool:
+        return True
+
+    assert_type(cb1.split(cb_split1), tuple[BaseExceptionGroup[SystemExit] | None, BaseExceptionGroup[SystemExit] | None])
+    assert_type(cb2.split(cb_split2), tuple[BaseExceptionGroup[ValueError] | None, BaseExceptionGroup[ValueError] | None])
+    cb1.split(cb_split2)  # type: ignore
+    cb2.split(cb_split1)  # type: ignore
+
+    # .derive()
+    # ---------
+
+    # Note, that `Self` type is not preserved in runtime.
+    assert_type(cb1.derive([ValueError()]), ExceptionGroup[ValueError])
+    assert_type(cb1.derive([KeyboardInterrupt()]), BaseExceptionGroup[KeyboardInterrupt])
+    assert_type(cb2.derive([ValueError()]), ExceptionGroup[ValueError])
+    assert_type(cb2.derive([KeyboardInterrupt()]), BaseExceptionGroup[KeyboardInterrupt])
+
+    # ExceptionGroup Custom Subclass
+    # ==============================
+
+    _E = TypeVar("_E", bound=Exception)
+
+    class CustomGroup(ExceptionGroup[_E]): ...
+
+    CustomGroup("x", [SystemExit()])  # type: ignore
+    cg1 = CustomGroup("x", [ValueError()])
+    assert_type(cg1, CustomGroup[ValueError])
+
+    # .subgroup()
+    # -----------
+
+    cg1.subgroup(BaseException)  # type: ignore
+    cg1.subgroup((KeyboardInterrupt, SystemExit))  # type: ignore
+
+    assert_type(cg1.subgroup(ValueError), ExceptionGroup[ValueError] | None)
+    assert_type(cg1.subgroup((KeyError,)), ExceptionGroup[KeyError] | None)
+
+    def cg_subgroup1(exc: ValueError | CustomGroup[ValueError]) -> bool:
+        return True
+
+    def cg_subgroup2(exc: ValueError) -> bool:
+        return True
+
+    assert_type(cg1.subgroup(cg_subgroup1), ExceptionGroup[ValueError] | None)
+    cg1.subgroup(cb_subgroup2)  # type: ignore
+
+    # .split()
+    # --------
+
+    assert_type(cg1.split(TypeError), tuple[ExceptionGroup[TypeError] | None, ExceptionGroup[ValueError] | None])
+    assert_type(cg1.split((TypeError,)), tuple[ExceptionGroup[TypeError] | None, ExceptionGroup[ValueError] | None])
+    cg1.split(BaseException)  # type: ignore
+
+    def cg_split1(exc: ValueError | CustomGroup[ValueError]) -> bool:
+        return True
+
+    def cg_split2(exc: ValueError) -> bool:
+        return True
+
+    assert_type(cg1.split(cg_split1), tuple[ExceptionGroup[ValueError] | None, ExceptionGroup[ValueError] | None])
+    cg1.split(cg_split2)  # type: ignore
+
+    # .derive()
+    # ---------
+
+    # Note, that `Self` type is not preserved in runtime.
+    assert_type(cg1.derive([ValueError()]), ExceptionGroup[ValueError])
+    assert_type(cg1.derive([KeyboardInterrupt()]), BaseExceptionGroup[KeyboardInterrupt])
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_iteration.py b/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_iteration.py
new file mode 100644
index 000000000000..3d609635377e
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_iteration.py
@@ -0,0 +1,16 @@
+from __future__ import annotations
+
+from typing import Iterator
+from typing_extensions import assert_type
+
+
+class OldStyleIter:
+    def __getitem__(self, index: int) -> str:
+        return str(index)
+
+
+for x in iter(OldStyleIter()):
+    assert_type(x, str)
+
+assert_type(iter(OldStyleIter()), Iterator[str])
+assert_type(next(iter(OldStyleIter())), str)
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_list.py b/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_list.py
new file mode 100644
index 000000000000..4113f5c66182
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_list.py
@@ -0,0 +1,21 @@
+from __future__ import annotations
+
+from typing import List, Union
+from typing_extensions import assert_type
+
+
+# list.__add__ example from #8292
+class Foo:
+    def asd(self) -> int:
+        return 1
+
+
+class Bar:
+    def asd(self) -> int:
+        return 2
+
+
+combined = [Foo()] + [Bar()]
+assert_type(combined, List[Union[Foo, Bar]])
+for item in combined:
+    assert_type(item.asd(), int)
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_object.py b/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_object.py
new file mode 100644
index 000000000000..60df1143f727
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_object.py
@@ -0,0 +1,13 @@
+from __future__ import annotations
+
+from typing import Any
+
+
+# The following should pass without error (see #6661):
+class Diagnostic:
+    def __reduce__(self) -> str | tuple[Any, ...]:
+        res = super().__reduce__()
+        if isinstance(res, tuple) and len(res) >= 3:
+            res[2]["_info"] = 42
+
+        return res
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_pow.py b/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_pow.py
new file mode 100644
index 000000000000..1f38710d6bea
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_pow.py
@@ -0,0 +1,91 @@
+from __future__ import annotations
+
+from decimal import Decimal
+from fractions import Fraction
+from typing import Any, Literal
+from typing_extensions import assert_type
+
+# See #7163
+assert_type(pow(1, 0), Literal[1])
+assert_type(1**0, Literal[1])
+assert_type(pow(1, 0, None), Literal[1])
+
+# TODO: We don't have a good way of expressing the fact
+# that passing 0 for the third argument will lead to an exception being raised
+# (see discussion in #8566)
+#
+# assert_type(pow(2, 4, 0), NoReturn)
+
+assert_type(pow(2, 4), int)
+assert_type(2**4, int)
+assert_type(pow(4, 6, None), int)
+
+assert_type(pow(5, -7), float)
+assert_type(5**-7, float)
+
+assert_type(pow(2, 4, 5), int)  # pow(<smallint>, <smallint>, <smallint>)
+assert_type(pow(2, 35, 3), int)  # pow(<smallint>, <bigint>, <smallint>)
+
+assert_type(pow(2, 8.5), float)
+assert_type(2**8.6, float)
+assert_type(pow(2, 8.6, None), float)
+
+# TODO: Why does this pass pyright but not mypy??
+# assert_type((-2) ** 0.5, complex)
+
+assert_type(pow((-5), 8.42, None), complex)
+
+assert_type(pow(4.6, 8), float)
+assert_type(4.6**8, float)
+assert_type(pow(5.1, 4, None), float)
+
+assert_type(pow(complex(6), 6.2), complex)
+assert_type(complex(6) ** 6.2, complex)
+assert_type(pow(complex(9), 7.3, None), complex)
+
+assert_type(pow(Fraction(), 4, None), Fraction)
+assert_type(Fraction() ** 4, Fraction)
+
+assert_type(pow(Fraction(3, 7), complex(1, 8)), complex)
+assert_type(Fraction(3, 7) ** complex(1, 8), complex)
+
+assert_type(pow(complex(4, -8), Fraction(2, 3)), complex)
+assert_type(complex(4, -8) ** Fraction(2, 3), complex)
+
+assert_type(pow(Decimal("1.0"), Decimal("1.6")), Decimal)
+assert_type(Decimal("1.0") ** Decimal("1.6"), Decimal)
+
+assert_type(pow(Decimal("1.0"), Decimal("1.0"), Decimal("1.0")), Decimal)
+assert_type(pow(Decimal("4.6"), 7, None), Decimal)
+assert_type(Decimal("4.6") ** 7, Decimal)
+
+# These would ideally be more precise, but `Any` is acceptable
+# They have to be `Any` due to the fact that type-checkers can't distinguish
+# between positive and negative numbers for the second argument to `pow()`
+#
+# int for positive 2nd-arg, float otherwise
+assert_type(pow(4, 65), Any)
+assert_type(pow(2, -45), Any)
+assert_type(pow(3, 57, None), Any)
+assert_type(pow(67, 0.98, None), Any)
+assert_type(87**7.32, Any)
+# pow(<pos-float>, <pos-or-neg-float>) -> float
+# pow(<neg-float>, <pos-or-neg-float>) -> complex
+assert_type(pow(4.7, 7.4), Any)
+assert_type(pow(-9.8, 8.3), Any)
+assert_type(pow(-9.3, -88.2), Any)
+assert_type(pow(8.2, -9.8), Any)
+assert_type(pow(4.7, 9.2, None), Any)
+# See #7046 -- float for a positive 1st arg, complex otherwise
+assert_type((-95) ** 8.42, Any)
+
+# All of the following cases should fail a type-checker.
+pow(1.9, 4, 6)  # type: ignore
+pow(4, 7, 4.32)  # type: ignore
+pow(6.2, 5.9, 73)  # type: ignore
+pow(complex(6), 6.2, 7)  # type: ignore
+pow(Fraction(), 5, 8)  # type: ignore
+Decimal("8.7") ** 3.14  # type: ignore
+
+# TODO: This fails at runtime, but currently passes mypy and pyright:
+pow(Decimal("8.5"), 3.21)
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_reversed.py b/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_reversed.py
new file mode 100644
index 000000000000..2a43a57deb4e
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_reversed.py
@@ -0,0 +1,34 @@
+from __future__ import annotations
+
+from collections.abc import Iterator
+from typing import Generic, TypeVar
+from typing_extensions import assert_type
+
+x: list[int] = []
+assert_type(list(reversed(x)), "list[int]")
+
+
+class MyReversible:
+    def __iter__(self) -> Iterator[str]:
+        yield "blah"
+
+    def __reversed__(self) -> Iterator[str]:
+        yield "blah"
+
+
+assert_type(list(reversed(MyReversible())), "list[str]")
+
+
+_T = TypeVar("_T")
+
+
+class MyLenAndGetItem(Generic[_T]):
+    def __len__(self) -> int:
+        return 0
+
+    def __getitem__(self, item: int) -> _T:
+        raise KeyError
+
+
+len_and_get_item: MyLenAndGetItem[int] = MyLenAndGetItem()
+assert_type(list(reversed(len_and_get_item)), "list[int]")
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_round.py b/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_round.py
new file mode 100644
index 000000000000..84081f3665b9
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_round.py
@@ -0,0 +1,68 @@
+from __future__ import annotations
+
+from typing import overload
+from typing_extensions import assert_type
+
+
+class CustomIndex:
+    def __index__(self) -> int:
+        return 1
+
+
+# float:
+
+assert_type(round(5.5), int)
+assert_type(round(5.5, None), int)
+assert_type(round(5.5, 0), float)
+assert_type(round(5.5, 1), float)
+assert_type(round(5.5, 5), float)
+assert_type(round(5.5, CustomIndex()), float)
+
+# int:
+
+assert_type(round(1), int)
+assert_type(round(1, 1), int)
+assert_type(round(1, None), int)
+assert_type(round(1, CustomIndex()), int)
+
+# Protocols:
+
+
+class WithCustomRound1:
+    def __round__(self) -> str:
+        return "a"
+
+
+assert_type(round(WithCustomRound1()), str)
+assert_type(round(WithCustomRound1(), None), str)
+# Errors:
+round(WithCustomRound1(), 1)  # type: ignore
+round(WithCustomRound1(), CustomIndex())  # type: ignore
+
+
+class WithCustomRound2:
+    def __round__(self, digits: int) -> str:
+        return "a"
+
+
+assert_type(round(WithCustomRound2(), 1), str)
+assert_type(round(WithCustomRound2(), CustomIndex()), str)
+# Errors:
+round(WithCustomRound2(), None)  # type: ignore
+round(WithCustomRound2())  # type: ignore
+
+
+class WithOverloadedRound:
+    @overload
+    def __round__(self, ndigits: None = ...) -> str: ...
+
+    @overload
+    def __round__(self, ndigits: int) -> bytes: ...
+
+    def __round__(self, ndigits: int | None = None) -> str | bytes:
+        return b"" if ndigits is None else ""
+
+
+assert_type(round(WithOverloadedRound()), str)
+assert_type(round(WithOverloadedRound(), None), str)
+assert_type(round(WithOverloadedRound(), 1), bytes)
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_sum.py b/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_sum.py
new file mode 100644
index 000000000000..cda7eadbbe41
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_sum.py
@@ -0,0 +1,55 @@
+from __future__ import annotations
+
+from typing import Any, List, Literal, Union
+from typing_extensions import assert_type
+
+
+class Foo:
+    def __add__(self, other: Any) -> Foo:
+        return Foo()
+
+
+class Bar:
+    def __radd__(self, other: Any) -> Bar:
+        return Bar()
+
+
+class Baz:
+    def __add__(self, other: Any) -> Baz:
+        return Baz()
+
+    def __radd__(self, other: Any) -> Baz:
+        return Baz()
+
+
+literal_list: list[Literal[0, 1]] = [0, 1, 1]
+
+assert_type(sum([2, 4]), int)
+assert_type(sum([3, 5], 4), int)
+
+assert_type(sum([True, False]), int)
+assert_type(sum([True, False], True), int)
+assert_type(sum(literal_list), int)
+
+assert_type(sum([["foo"], ["bar"]], ["baz"]), List[str])
+
+assert_type(sum([Foo(), Foo()], Foo()), Foo)
+assert_type(sum([Baz(), Baz()]), Union[Baz, Literal[0]])
+
+# mypy and pyright infer the types differently for these, so we can't use assert_type
+# Just test that no error is emitted for any of these
+sum([("foo",), ("bar", "baz")], ())  # mypy: `tuple[str, ...]`; pyright: `tuple[()] | tuple[str] | tuple[str, str]`
+sum([5.6, 3.2])  # mypy: `float`; pyright: `float | Literal[0]`
+sum([2.5, 5.8], 5)  # mypy: `float`; pyright: `float | int`
+
+# These all fail at runtime
+sum("abcde")  # type: ignore
+sum([["foo"], ["bar"]])  # type: ignore
+sum([("foo",), ("bar", "baz")])  # type: ignore
+sum([Foo(), Foo()])  # type: ignore
+sum([Bar(), Bar()], Bar())  # type: ignore
+sum([Bar(), Bar()])  # type: ignore
+
+# TODO: these pass pyright with the current stubs, but mypy erroneously emits an error:
+# sum([3, Fraction(7, 22), complex(8, 0), 9.83])
+# sum([3, Decimal('0.98')])
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_tuple.py b/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_tuple.py
new file mode 100644
index 000000000000..bc0d8db28389
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/builtins/check_tuple.py
@@ -0,0 +1,13 @@
+from __future__ import annotations
+
+from typing import Tuple
+from typing_extensions import assert_type
+
+
+# Empty tuples, see #8275
+class TupleSub(Tuple[int, ...]):
+    pass
+
+
+assert_type(TupleSub(), TupleSub)
+assert_type(TupleSub([1, 2, 3]), TupleSub)
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/check_codecs.py b/mypy/typeshed/stdlib/@tests/test_cases/check_codecs.py
new file mode 100644
index 000000000000..19e663ceeaaf
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/check_codecs.py
@@ -0,0 +1,13 @@
+from __future__ import annotations
+
+import codecs
+from typing_extensions import assert_type
+
+assert_type(codecs.decode("x", "unicode-escape"), str)
+assert_type(codecs.decode(b"x", "unicode-escape"), str)
+
+assert_type(codecs.decode(b"x", "utf-8"), str)
+codecs.decode("x", "utf-8")  # type: ignore
+
+assert_type(codecs.decode("ab", "hex"), bytes)
+assert_type(codecs.decode(b"ab", "hex"), bytes)
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/check_concurrent_futures.py b/mypy/typeshed/stdlib/@tests/test_cases/check_concurrent_futures.py
new file mode 100644
index 000000000000..962ec23c6b48
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/check_concurrent_futures.py
@@ -0,0 +1,30 @@
+from __future__ import annotations
+
+from collections.abc import Callable, Iterator
+from concurrent.futures import Future, ThreadPoolExecutor, as_completed
+from typing_extensions import assert_type
+
+
+class Parent: ...
+
+
+class Child(Parent): ...
+
+
+def check_as_completed_covariance() -> None:
+    with ThreadPoolExecutor() as executor:
+        f1 = executor.submit(lambda: Parent())
+        f2 = executor.submit(lambda: Child())
+        fs: list[Future[Parent] | Future[Child]] = [f1, f2]
+        assert_type(as_completed(fs), Iterator[Future[Parent]])
+        for future in as_completed(fs):
+            assert_type(future.result(), Parent)
+
+
+def check_future_invariance() -> None:
+    def execute_callback(callback: Callable[[], Parent], future: Future[Parent]) -> None:
+        future.set_result(callback())
+
+    fut: Future[Child] = Future()
+    execute_callback(lambda: Parent(), fut)  # type: ignore
+    assert isinstance(fut.result(), Child)
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/check_contextlib.py b/mypy/typeshed/stdlib/@tests/test_cases/check_contextlib.py
new file mode 100644
index 000000000000..648661bca856
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/check_contextlib.py
@@ -0,0 +1,20 @@
+from __future__ import annotations
+
+from contextlib import ExitStack
+from typing_extensions import assert_type
+
+
+# See issue #7961
+class Thing(ExitStack):
+    pass
+
+
+stack = ExitStack()
+thing = Thing()
+assert_type(stack.enter_context(Thing()), Thing)
+assert_type(thing.enter_context(ExitStack()), ExitStack)
+
+with stack as cm:
+    assert_type(cm, ExitStack)
+with thing as cm2:
+    assert_type(cm2, Thing)
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/check_dataclasses.py b/mypy/typeshed/stdlib/@tests/test_cases/check_dataclasses.py
new file mode 100644
index 000000000000..76ce8e1bd260
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/check_dataclasses.py
@@ -0,0 +1,101 @@
+from __future__ import annotations
+
+import dataclasses as dc
+from typing import TYPE_CHECKING, Any, Dict, FrozenSet, Tuple, Type, Union
+from typing_extensions import Annotated, assert_type
+
+if TYPE_CHECKING:
+    from _typeshed import DataclassInstance
+
+
+@dc.dataclass
+class Foo:
+    attr: str
+
+
+assert_type(dc.fields(Foo), Tuple[dc.Field[Any], ...])
+
+# Mypy correctly emits errors on these
+# due to the fact it's a dataclass class, not an instance.
+# Pyright, however, handles ClassVar members in protocols differently.
+# See https://github.com/microsoft/pyright/issues/4339
+#
+# dc.asdict(Foo)
+# dc.astuple(Foo)
+# dc.replace(Foo)
+
+# See #9723 for why we can't make this assertion
+# if dc.is_dataclass(Foo):
+#     assert_type(Foo, Type[Foo])
+
+f = Foo(attr="attr")
+
+assert_type(dc.fields(f), Tuple[dc.Field[Any], ...])
+assert_type(dc.asdict(f), Dict[str, Any])
+assert_type(dc.astuple(f), Tuple[Any, ...])
+assert_type(dc.replace(f, attr="new"), Foo)
+
+if dc.is_dataclass(f):
+    # The inferred type doesn't change
+    # if it's already known to be a subtype of _DataclassInstance
+    assert_type(f, Foo)
+
+
+def check_other_isdataclass_overloads(x: type, y: object) -> None:
+    # TODO: pyright correctly emits an error on this, but mypy does not -- why?
+    # dc.fields(x)
+
+    dc.fields(y)  # type: ignore
+
+    dc.asdict(x)  # type: ignore
+    dc.asdict(y)  # type: ignore
+
+    dc.astuple(x)  # type: ignore
+    dc.astuple(y)  # type: ignore
+
+    dc.replace(x)  # type: ignore
+    dc.replace(y)  # type: ignore
+
+    if dc.is_dataclass(x):
+        assert_type(x, Type["DataclassInstance"])
+        assert_type(dc.fields(x), Tuple[dc.Field[Any], ...])
+
+        # Mypy correctly emits an error on these due to the fact
+        # that it's a dataclass class, not a dataclass instance.
+        # Pyright, however, handles ClassVar members in protocols differently.
+        # See https://github.com/microsoft/pyright/issues/4339
+        #
+        # dc.asdict(x)
+        # dc.astuple(x)
+        # dc.replace(x)
+
+    if dc.is_dataclass(y):
+        assert_type(y, Union["DataclassInstance", Type["DataclassInstance"]])
+        assert_type(dc.fields(y), Tuple[dc.Field[Any], ...])
+
+        # Mypy correctly emits an error on these due to the fact we don't know
+        # whether it's a dataclass class or a dataclass instance.
+        # Pyright, however, handles ClassVar members in protocols differently.
+        # See https://github.com/microsoft/pyright/issues/4339
+        #
+        # dc.asdict(y)
+        # dc.astuple(y)
+        # dc.replace(y)
+
+    if dc.is_dataclass(y) and not isinstance(y, type):
+        assert_type(y, "DataclassInstance")
+        assert_type(dc.fields(y), Tuple[dc.Field[Any], ...])
+        assert_type(dc.asdict(y), Dict[str, Any])
+        assert_type(dc.astuple(y), Tuple[Any, ...])
+        dc.replace(y)
+
+
+# Regression test for #11653
+D = dc.make_dataclass(
+    "D", [("a", Union[int, None]), "y", ("z", Annotated[FrozenSet[bytes], "metadata"], dc.field(default=frozenset({b"foo"})))]
+)
+# Check that it's inferred by the type checker as a class object of some kind
+# (but don't assert the exact type that `D` is inferred as,
+# in case a type checker decides to add some special-casing for
+# `make_dataclass` in the future)
+assert_type(D.__mro__, Tuple[type, ...])
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/check_enum.py b/mypy/typeshed/stdlib/@tests/test_cases/check_enum.py
new file mode 100644
index 000000000000..4ea4947c811d
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/check_enum.py
@@ -0,0 +1,38 @@
+from __future__ import annotations
+
+import enum
+import sys
+from typing import Literal, Type
+from typing_extensions import assert_type
+
+A = enum.Enum("A", "spam eggs bacon")
+B = enum.Enum("B", ["spam", "eggs", "bacon"])
+C = enum.Enum("Bar", [("spam", 1), ("eggs", 2), ("bacon", 3)])
+D = enum.Enum("Bar", {"spam": 1, "eggs": 2})
+
+assert_type(A, Type[A])
+assert_type(B, Type[B])
+assert_type(C, Type[C])
+assert_type(D, Type[D])
+
+
+class EnumOfTuples(enum.Enum):
+    X = 1, 2, 3
+    Y = 4, 5, 6
+
+
+assert_type(EnumOfTuples((1, 2, 3)), EnumOfTuples)
+
+# TODO: ideally this test would pass:
+#
+# if sys.version_info >= (3, 12):
+#     assert_type(EnumOfTuples(1, 2, 3), EnumOfTuples)
+
+
+if sys.version_info >= (3, 11):
+
+    class Foo(enum.StrEnum):
+        X = enum.auto()
+
+    assert_type(Foo.X, Literal[Foo.X])
+    assert_type(Foo.X.value, str)
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/check_functools.py b/mypy/typeshed/stdlib/@tests/test_cases/check_functools.py
new file mode 100644
index 000000000000..dca572683f8d
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/check_functools.py
@@ -0,0 +1,67 @@
+from __future__ import annotations
+
+from functools import cached_property, wraps
+from typing import Callable, TypeVar
+from typing_extensions import ParamSpec, assert_type
+
+P = ParamSpec("P")
+T_co = TypeVar("T_co", covariant=True)
+
+
+def my_decorator(func: Callable[P, T_co]) -> Callable[P, T_co]:
+    @wraps(func)
+    def wrapper(*args: P.args, **kwargs: P.kwargs) -> T_co:
+        print(args)
+        return func(*args, **kwargs)
+
+    # verify that the wrapped function has all these attributes
+    wrapper.__annotations__ = func.__annotations__
+    wrapper.__doc__ = func.__doc__
+    wrapper.__module__ = func.__module__
+    wrapper.__name__ = func.__name__
+    wrapper.__qualname__ = func.__qualname__
+    return wrapper
+
+
+class A:
+    def __init__(self, x: int):
+        self.x = x
+
+    @cached_property
+    def x(self) -> int:
+        return 0
+
+
+assert_type(A(x=1).x, int)
+
+
+class B:
+    @cached_property
+    def x(self) -> int:
+        return 0
+
+
+def check_cached_property_settable(x: int) -> None:
+    b = B()
+    assert_type(b.x, int)
+    b.x = x
+    assert_type(b.x, int)
+
+
+# https://github.com/python/typeshed/issues/10048
+class Parent: ...
+
+
+class Child(Parent): ...
+
+
+class X:
+    @cached_property
+    def some(self) -> Parent:
+        return Parent()
+
+
+class Y(X):
+    @cached_property
+    def some(self) -> Child:  # safe override
+        return Child()
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/check_importlib.py b/mypy/typeshed/stdlib/@tests/test_cases/check_importlib.py
new file mode 100644
index 000000000000..17eefdafc971
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/check_importlib.py
@@ -0,0 +1,47 @@
+from __future__ import annotations
+
+import importlib.abc
+import importlib.util
+import pathlib
+import sys
+import zipfile
+from collections.abc import Sequence
+from importlib.machinery import ModuleSpec
+from types import ModuleType
+from typing_extensions import Self
+
+# Assert that some Path classes are Traversable.
+if sys.version_info >= (3, 9):
+
+    def traverse(t: importlib.abc.Traversable) -> None:
+        pass
+
+    traverse(pathlib.Path())
+    traverse(zipfile.Path(""))
+
+
+class MetaFinder:
+    @classmethod
+    def find_spec(cls, fullname: str, path: Sequence[str] | None, target: ModuleType | None = None) -> ModuleSpec | None:
+        return None  # simplified mock for demonstration purposes only
+
+
+class PathFinder:
+    @classmethod
+    def path_hook(cls, path_entry: str) -> type[Self]:
+        return cls  # simplified mock for demonstration purposes only
+
+    @classmethod
+    def find_spec(cls, fullname: str, target: ModuleType | None = None) -> ModuleSpec | None:
+        return None  # simplified mock for demonstration purposes only
+
+
+class Loader:
+    @classmethod
+    def load_module(cls, fullname: str) -> ModuleType:
+        return ModuleType(fullname)
+
+
+sys.meta_path.append(MetaFinder)
+sys.path_hooks.append(PathFinder.path_hook)
+importlib.util.spec_from_loader("xxxx42xxxx", Loader)
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/check_importlib_metadata.py b/mypy/typeshed/stdlib/@tests/test_cases/check_importlib_metadata.py
new file mode 100644
index 000000000000..f1322e16c54f
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/check_importlib_metadata.py
@@ -0,0 +1,33 @@
+from __future__ import annotations
+
+import sys
+from _typeshed import StrPath
+from os import PathLike
+from pathlib import Path
+from typing import Any
+from zipfile import Path as ZipPath
+
+if sys.version_info >= (3, 10):
+    from importlib.metadata._meta import SimplePath
+
+    # Simplified version of zipfile.Path
+    class MyPath:
+        @property
+        def parent(self) -> PathLike[str]: ...  # undocumented
+
+        def read_text(self, encoding: str | None = ..., errors: str | None = ...) -> str: ...
+        def joinpath(self, *other: StrPath) -> MyPath: ...
+        def __truediv__(self, add: StrPath) -> MyPath: ...
+
+    if sys.version_info >= (3, 12):
+
+        def takes_simple_path(p: SimplePath[Any]) -> None: ...
+
+    else:
+
+        def takes_simple_path(p: SimplePath) -> None: ...
+
+    takes_simple_path(Path())
+    takes_simple_path(ZipPath(""))
+    takes_simple_path(MyPath())
+    takes_simple_path("some string")  # type: ignore
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/check_io.py b/mypy/typeshed/stdlib/@tests/test_cases/check_io.py
new file mode 100644
index 000000000000..abf84dd5a103
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/check_io.py
@@ -0,0 +1,6 @@
+from gzip import GzipFile
+from io import FileIO, TextIOWrapper
+
+TextIOWrapper(FileIO(""))
+TextIOWrapper(FileIO(13))
+TextIOWrapper(GzipFile(""))
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/check_logging.py b/mypy/typeshed/stdlib/@tests/test_cases/check_logging.py
new file mode 100644
index 000000000000..fe3d8eb16fd0
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/check_logging.py
@@ -0,0 +1,30 @@
+from __future__ import annotations
+
+import logging
+import logging.handlers
+import multiprocessing
+import queue
+from typing import Any
+
+# This pattern comes from the logging docs, and should therefore pass a type checker
+# See https://docs.python.org/3/library/logging.html#logrecord-objects
+
+old_factory = logging.getLogRecordFactory()
+
+
+def record_factory(*args: Any, **kwargs: Any) -> logging.LogRecord:
+    record = old_factory(*args, **kwargs)
+    record.custom_attribute = 0xDECAFBAD
+    return record
+
+
+logging.setLogRecordFactory(record_factory)
+
+# The logging docs say that QueueHandler and QueueListener can take "any queue-like object"
+# We test that here (regression test for #10168)
+logging.handlers.QueueHandler(queue.Queue())
+logging.handlers.QueueHandler(queue.SimpleQueue())
+logging.handlers.QueueHandler(multiprocessing.Queue())
+logging.handlers.QueueListener(queue.Queue())
+logging.handlers.QueueListener(queue.SimpleQueue())
+logging.handlers.QueueListener(multiprocessing.Queue())
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/check_multiprocessing.py b/mypy/typeshed/stdlib/@tests/test_cases/check_multiprocessing.py
new file mode 100644
index 000000000000..201f96c0c4c8
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/check_multiprocessing.py
@@ -0,0 +1,14 @@
+from __future__ import annotations
+
+from ctypes import c_char, c_float
+from multiprocessing import Array, Value
+from multiprocessing.sharedctypes import Synchronized, SynchronizedString
+from typing_extensions import assert_type
+
+string = Array(c_char, 12)
+assert_type(string, SynchronizedString)
+assert_type(string.value, bytes)
+
+field = Value(c_float, 0.0)
+assert_type(field, Synchronized[float])
+field.value = 1.2
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/check_pathlib.py b/mypy/typeshed/stdlib/@tests/test_cases/check_pathlib.py
new file mode 100644
index 000000000000..0b52c3669d07
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/check_pathlib.py
@@ -0,0 +1,20 @@
+from __future__ import annotations
+
+from pathlib import Path, PureWindowsPath
+
+if Path("asdf") == Path("asdf"):
+    ...
+
+# https://github.com/python/typeshed/issues/10661
+# Provide a true positive error when comparing Path to str
+# mypy should report a comparison-overlap error with --strict-equality,
+# and pyright should report a reportUnnecessaryComparison error
+if Path("asdf") == "asdf":  # type: ignore
+    ...
+
+# Errors on comparison here are technically false positives. However, this comparison is a little
+# interesting: it can never hold true on Posix, but could hold true on Windows. We should experiment
+# with more accurate __new__, such that we only get an error for such comparisons on platforms
+# where they can never hold true.
+if PureWindowsPath("asdf") == Path("asdf"):  # type: ignore
+    ...
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/check_re.py b/mypy/typeshed/stdlib/@tests/test_cases/check_re.py
new file mode 100644
index 000000000000..b6ab2b0d59d2
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/check_re.py
@@ -0,0 +1,26 @@
+from __future__ import annotations
+
+import mmap
+import re
+import typing as t
+from typing_extensions import assert_type
+
+
+def check_search(str_pat: re.Pattern[str], bytes_pat: re.Pattern[bytes]) -> None:
+    assert_type(str_pat.search("x"), t.Optional[t.Match[str]])
+    assert_type(bytes_pat.search(b"x"), t.Optional[t.Match[bytes]])
+    assert_type(bytes_pat.search(bytearray(b"x")), t.Optional[t.Match[bytes]])
+    assert_type(bytes_pat.search(mmap.mmap(0, 10)), t.Optional[t.Match[bytes]])
+
+
+def check_search_with_AnyStr(pattern: re.Pattern[t.AnyStr], string: t.AnyStr) -> re.Match[t.AnyStr]:
+    """See issue #9591"""
+    match = pattern.search(string)
+    if match is None:
+        raise ValueError(f"'{string!r}' does not match {pattern!r}")
+    return match
+
+
+def check_no_ReadableBuffer_false_negatives() -> None:
+    re.compile("foo").search(bytearray(b"foo"))  # type: ignore
+    re.compile("foo").search(mmap.mmap(0, 10))  # type: ignore
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/check_sqlite3.py b/mypy/typeshed/stdlib/@tests/test_cases/check_sqlite3.py
new file mode 100644
index 000000000000..3ec47ceccb90
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/check_sqlite3.py
@@ -0,0 +1,26 @@
+from __future__ import annotations
+
+import sqlite3
+from typing_extensions import assert_type
+
+
+class MyConnection(sqlite3.Connection):
+    pass
+
+
+# Default return-type is Connection.
+assert_type(sqlite3.connect(":memory:"), sqlite3.Connection)
+
+# Providing an alternate factory changes the return-type.
+assert_type(sqlite3.connect(":memory:", factory=MyConnection), MyConnection)
+
+# Provides a true positive error. When checking the connect() function,
+# mypy should report an arg-type error for the factory argument.
+with sqlite3.connect(":memory:", factory=None) as con:  # type: ignore
+    pass
+
+# The Connection class also accepts a `factory` arg but it does not affect
+# the return-type. This use case is not idiomatic--connections should be
+# established using the `connect()` function, not directly (as shown here).
+assert_type(sqlite3.Connection(":memory:", factory=None), sqlite3.Connection)
+assert_type(sqlite3.Connection(":memory:", factory=MyConnection), sqlite3.Connection)
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/check_tarfile.py b/mypy/typeshed/stdlib/@tests/test_cases/check_tarfile.py
new file mode 100644
index 000000000000..54510a3d7626
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/check_tarfile.py
@@ -0,0 +1,13 @@
+import tarfile
+
+with tarfile.open("test.tar.xz", "w:xz") as tar:
+    pass
+
+# Test with valid preset values
+tarfile.open("test.tar.xz", "w:xz", preset=0)
+tarfile.open("test.tar.xz", "w:xz", preset=5)
+tarfile.open("test.tar.xz", "w:xz", preset=9)
+
+# Test with invalid preset values
+tarfile.open("test.tar.xz", "w:xz", preset=-1)  # type: ignore
+tarfile.open("test.tar.xz", "w:xz", preset=10)  # type: ignore
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/check_tempfile.py b/mypy/typeshed/stdlib/@tests/test_cases/check_tempfile.py
new file mode 100644
index 000000000000..c259c192a140
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/check_tempfile.py
@@ -0,0 +1,31 @@
+from __future__ import annotations
+
+import io
+import sys
+from tempfile import TemporaryFile, _TemporaryFileWrapper
+from typing_extensions import assert_type
+
+if sys.platform == "win32":
+    assert_type(TemporaryFile(), _TemporaryFileWrapper[bytes])
+    assert_type(TemporaryFile("w+"), _TemporaryFileWrapper[str])
+    assert_type(TemporaryFile("w+b"), _TemporaryFileWrapper[bytes])
+    assert_type(TemporaryFile("wb"), _TemporaryFileWrapper[bytes])
+    assert_type(TemporaryFile("rb"), _TemporaryFileWrapper[bytes])
+    assert_type(TemporaryFile("wb", 0), _TemporaryFileWrapper[bytes])
+    assert_type(TemporaryFile(mode="w+"), _TemporaryFileWrapper[str])
+    assert_type(TemporaryFile(mode="w+b"), _TemporaryFileWrapper[bytes])
+    assert_type(TemporaryFile(mode="wb"), _TemporaryFileWrapper[bytes])
+    assert_type(TemporaryFile(mode="rb"), _TemporaryFileWrapper[bytes])
+    assert_type(TemporaryFile(buffering=0), _TemporaryFileWrapper[bytes])
+else:
+    assert_type(TemporaryFile(), io.BufferedRandom)
+    assert_type(TemporaryFile("w+"), io.TextIOWrapper)
+    assert_type(TemporaryFile("w+b"), io.BufferedRandom)
+    assert_type(TemporaryFile("wb"), io.BufferedWriter)
+    assert_type(TemporaryFile("rb"), io.BufferedReader)
+    assert_type(TemporaryFile("wb", 0), io.FileIO)
+    assert_type(TemporaryFile(mode="w+"), io.TextIOWrapper)
+    assert_type(TemporaryFile(mode="w+b"), io.BufferedRandom)
+    assert_type(TemporaryFile(mode="wb"), io.BufferedWriter)
+    assert_type(TemporaryFile(mode="rb"), io.BufferedReader)
+    assert_type(TemporaryFile(buffering=0), io.FileIO)
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/check_threading.py b/mypy/typeshed/stdlib/@tests/test_cases/check_threading.py
new file mode 100644
index 000000000000..eddfc2549a64
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/check_threading.py
@@ -0,0 +1,14 @@
+from __future__ import annotations
+
+import _threading_local
+import threading
+
+loc = threading.local()
+loc.foo = 42
+del loc.foo
+loc.baz = ["spam", "eggs"]
+del loc.baz
+
+l2 = _threading_local.local()
+l2.asdfasdf = 56
+del l2.asdfasdf
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/check_tkinter.py b/mypy/typeshed/stdlib/@tests/test_cases/check_tkinter.py
new file mode 100644
index 000000000000..befac6697519
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/check_tkinter.py
@@ -0,0 +1,30 @@
+from __future__ import annotations
+
+import tkinter
+import traceback
+import types
+
+
+def custom_handler(exc: type[BaseException], val: BaseException, tb: types.TracebackType | None) -> None:
+    print("oh no")
+
+
+root = tkinter.Tk()
+root.report_callback_exception = traceback.print_exception
+root.report_callback_exception = custom_handler
+
+
+def foo(x: int, y: str) -> None:
+    pass
+
+
+root.after(1000, foo, 10, "lol")
+root.after(1000, foo, 10, 10)  # type: ignore
+
+
+# Font size must be integer
+label = tkinter.Label()
+label.config(font=("", 12))
+label.config(font=("", 12.34))  # type: ignore
+label.config(font=("", 12, "bold"))
+label.config(font=("", 12.34, "bold"))  # type: ignore
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/check_unittest.py b/mypy/typeshed/stdlib/@tests/test_cases/check_unittest.py
new file mode 100644
index 000000000000..40c6efaa8ca0
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/check_unittest.py
@@ -0,0 +1,173 @@
+from __future__ import annotations
+
+import unittest
+from collections.abc import Iterator, Mapping
+from datetime import datetime, timedelta
+from decimal import Decimal
+from fractions import Fraction
+from typing import TypedDict
+from typing_extensions import assert_type
+from unittest.mock import MagicMock, Mock, patch
+
+case = unittest.TestCase()
+
+###
+# Tests for assertAlmostEqual
+###
+
+case.assertAlmostEqual(1, 2.4)
+case.assertAlmostEqual(2.4, 2.41)
+case.assertAlmostEqual(Fraction(49, 50), Fraction(48, 50))
+case.assertAlmostEqual(3.14, complex(5, 6))
+case.assertAlmostEqual(datetime(1999, 1, 2), datetime(1999, 1, 2, microsecond=1), delta=timedelta(hours=1))
+case.assertAlmostEqual(datetime(1999, 1, 2), datetime(1999, 1, 2, microsecond=1), None, "foo", timedelta(hours=1))
+case.assertAlmostEqual(Decimal("1.1"), Decimal("1.11"))
+case.assertAlmostEqual(2.4, 2.41, places=8)
+case.assertAlmostEqual(2.4, 2.41, delta=0.02)
+case.assertAlmostEqual(2.4, 2.41, None, "foo", 0.02)
+
+case.assertAlmostEqual(2.4, 2.41, places=9, delta=0.02)  # type: ignore
+case.assertAlmostEqual("foo", "bar")  # type: ignore
+case.assertAlmostEqual(datetime(1999, 1, 2), datetime(1999, 1, 2, microsecond=1))  # type: ignore
+case.assertAlmostEqual(Decimal("0.4"), Fraction(1, 2))  # type: ignore
+case.assertAlmostEqual(complex(2, 3), Decimal("0.9"))  # type: ignore
+
+###
+# Tests for assertNotAlmostEqual
+###
+
+case.assertAlmostEqual(1, 2.4)
+case.assertNotAlmostEqual(Fraction(49, 50), Fraction(48, 50))
+case.assertAlmostEqual(3.14, complex(5, 6))
+case.assertNotAlmostEqual(datetime(1999, 1, 2), datetime(1999, 1, 2, microsecond=1), delta=timedelta(hours=1))
+case.assertNotAlmostEqual(datetime(1999, 1, 2), datetime(1999, 1, 2, microsecond=1), None, "foo", timedelta(hours=1))
+
+case.assertNotAlmostEqual(2.4, 2.41, places=9, delta=0.02)  # type: ignore
+case.assertNotAlmostEqual("foo", "bar")  # type: ignore
+case.assertNotAlmostEqual(datetime(1999, 1, 2), datetime(1999, 1, 2, microsecond=1))  # type: ignore
+case.assertNotAlmostEqual(Decimal("0.4"), Fraction(1, 2))  # type: ignore
+case.assertNotAlmostEqual(complex(2, 3), Decimal("0.9"))  # type: ignore
+
+###
+# Tests for assertGreater
+###
+
+
+class Spam:
+    def __lt__(self, other: object) -> bool:
+        return True
+
+
+class Eggs:
+    def __gt__(self, other: object) -> bool:
+        return True
+
+
+class Ham:
+    def __lt__(self, other: Ham) -> bool:
+        if not isinstance(other, Ham):
+            return NotImplemented
+        return True
+
+
+class Bacon:
+    def __gt__(self, other: Bacon) -> bool:
+        if not isinstance(other, Bacon):
+            return NotImplemented
+        return True
+
+
+case.assertGreater(5.8, 3)
+case.assertGreater(Decimal("4.5"), Fraction(3, 2))
+case.assertGreater(Fraction(3, 2), 0.9)
+case.assertGreater(Eggs(), object())
+case.assertGreater(object(), Spam())
+case.assertGreater(Ham(), Ham())
+case.assertGreater(Bacon(), Bacon())
+
+case.assertGreater(object(), object())  # type: ignore
+case.assertGreater(datetime(1999, 1, 2), 1)  # type: ignore
+case.assertGreater(Spam(), Eggs())  # type: ignore
+case.assertGreater(Ham(), Bacon())  # type: ignore
+case.assertGreater(Bacon(), Ham())  # type: ignore
+
+
+###
+# Tests for assertDictEqual
+###
+
+
+class TD1(TypedDict):
+    x: int
+    y: str
+
+
+class TD2(TypedDict):
+    a: bool
+    b: bool
+
+
+class MyMapping(Mapping[str, int]):
+    def __getitem__(self, __key: str) -> int:
+        return 42
+
+    def __iter__(self) -> Iterator[str]:
+        return iter([])
+
+    def __len__(self) -> int:
+        return 0
+
+
+td1: TD1 = {"x": 1, "y": "foo"}
+td2: TD2 = {"a": True, "b": False}
+m = MyMapping()
+
+case.assertDictEqual({}, {})
+case.assertDictEqual({"x": 1, "y": 2}, {"x": 1, "y": 2})
+case.assertDictEqual({"x": 1, "y": "foo"}, {"y": "foo", "x": 1})
+case.assertDictEqual({"x": 1}, {})
+case.assertDictEqual({}, {"x": 1})
+case.assertDictEqual({1: "x"}, {"y": 222})
+case.assertDictEqual({1: "x"}, td1)
+case.assertDictEqual(td1, {1: "x"})
+case.assertDictEqual(td1, td2)
+
+case.assertDictEqual(1, {})  # type: ignore
+case.assertDictEqual({}, 1)  # type: ignore
+
+# These should fail, but don't due to TypedDict limitations:
+# case.assertDictEqual(m, {"": 0})  # xtype: ignore
+# case.assertDictEqual({"": 0}, m)  # xtype: ignore
+
+###
+# Tests for mock.patch
+###
+
+
+@patch("sys.exit")
+def f_default_new(i: int, mock: MagicMock) -> str:
+    return "asdf"
+
+
+@patch("sys.exit", new=42)
+def f_explicit_new(i: int) -> str:
+    return "asdf"
+
+
+assert_type(f_default_new(1), str)
+f_default_new("a")  # Not an error due to ParamSpec limitations
+assert_type(f_explicit_new(1), str)
+f_explicit_new("a")  # type: ignore[arg-type]
+
+
+@patch("sys.exit", new=Mock())
+class TestXYZ(unittest.TestCase):
+    attr: int = 5
+
+    @staticmethod
+    def method() -> int:
+        return 123
+
+
+assert_type(TestXYZ.attr, int)
+assert_type(TestXYZ.method(), int)
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/check_xml.py b/mypy/typeshed/stdlib/@tests/test_cases/check_xml.py
new file mode 100644
index 000000000000..b485dac8dc29
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/check_xml.py
@@ -0,0 +1,35 @@
+from __future__ import annotations
+
+import sys
+from typing_extensions import assert_type
+from xml.dom.minidom import Document
+
+document = Document()
+
+assert_type(document.toxml(), str)
+assert_type(document.toxml(encoding=None), str)
+assert_type(document.toxml(encoding="UTF8"), bytes)
+assert_type(document.toxml("UTF8"), bytes)
+if sys.version_info >= (3, 9):
+    assert_type(document.toxml(standalone=True), str)
+    assert_type(document.toxml("UTF8", True), bytes)
+    assert_type(document.toxml(encoding="UTF8", standalone=True), bytes)
+
+
+# Because toprettyxml can mix positional and keyword variants of the "encoding" argument, which
+# determines the return type, the proper stub typing isn't immediately obvious. This is a basic
+# brute-force sanity check.
+# Test cases like toxml
+assert_type(document.toprettyxml(), str)
+assert_type(document.toprettyxml(encoding=None), str)
+assert_type(document.toprettyxml(encoding="UTF8"), bytes)
+if sys.version_info >= (3, 9):
+    assert_type(document.toprettyxml(standalone=True), str)
+    assert_type(document.toprettyxml(encoding="UTF8", standalone=True), bytes)
+# Test cases unique to toprettyxml
+assert_type(document.toprettyxml("  "), str)
+assert_type(document.toprettyxml("  ", "\r\n"), str)
+assert_type(document.toprettyxml("  ", "\r\n", "UTF8"), bytes)
+if sys.version_info >= (3, 9):
+    assert_type(document.toprettyxml("  ", "\r\n", "UTF8", True), bytes)
+    assert_type(document.toprettyxml("  ", "\r\n", standalone=True), str)
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/collections/check_defaultdict-py39.py b/mypy/typeshed/stdlib/@tests/test_cases/collections/check_defaultdict-py39.py
new file mode 100644
index 000000000000..9fe5ec8076ce
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/collections/check_defaultdict-py39.py
@@ -0,0 +1,69 @@
+"""
+Tests for `defaultdict.__or__` and `defaultdict.__ror__`.
+These methods were only added in py39.
+"""
+
+from __future__ import annotations
+
+import os
+import sys
+from collections import defaultdict
+from typing import Mapping, TypeVar, Union
+from typing_extensions import Self, assert_type
+
+_KT = TypeVar("_KT")
+_VT = TypeVar("_VT")
+
+
+if sys.version_info >= (3, 9):
+
+    class CustomDefaultDictSubclass(defaultdict[_KT, _VT]):
+        pass
+
+    class CustomMappingWithDunderOr(Mapping[_KT, _VT]):
+        def __or__(self, other: Mapping[_KT, _VT]) -> dict[_KT, _VT]:
+            return {}
+
+        def __ror__(self, other: Mapping[_KT, _VT]) -> dict[_KT, _VT]:
+            return {}
+
+        def __ior__(self, other: Mapping[_KT, _VT]) -> Self:
+            return self
+
+    def test_defaultdict_dot_or(
+        a: defaultdict[int, int],
+        b: CustomDefaultDictSubclass[int, int],
+        c: defaultdict[str, str],
+        d: Mapping[int, int],
+        e: CustomMappingWithDunderOr[str, str],
+    ) -> None:
+        assert_type(a | b, defaultdict[int, int])
+
+        # In contrast to `dict.__or__`, `defaultdict.__or__` returns `Self` if called on a subclass of `defaultdict`:
+        assert_type(b | a, CustomDefaultDictSubclass[int, int])
+
+        assert_type(a | c, defaultdict[Union[int, str], Union[int, str]])
+
+        # arbitrary mappings are not accepted by `defaultdict.__or__`;
+        # it has to be a subclass of `dict`
+        a | d  # type: ignore
+
+        # but Mappings such as `os._Environ` or `CustomMappingWithDunderOr`,
+        # which define `__ror__` methods that accept `dict`, are fine
+        # (`os._Environ.__(r)or__` always returns `dict`, even if a `defaultdict` is passed):
+        assert_type(a | os.environ, dict[Union[str, int], Union[str, int]])
+        assert_type(os.environ | a, dict[Union[str, int], Union[str, int]])
+
+        assert_type(c | os.environ, dict[str, str])
+        assert_type(c | e, dict[str, str])
+
+        assert_type(os.environ | c, dict[str, str])
+        assert_type(e | c, dict[str, str])
+
+        e |= c
+        e |= a  # type: ignore
+
+        # TODO: this test passes mypy, but fails pyright for some reason:
+        # c |= e
+
+        c |= a  # type: ignore
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/email/check_message.py b/mypy/typeshed/stdlib/@tests/test_cases/email/check_message.py
new file mode 100644
index 000000000000..a9b43e23fb27
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/email/check_message.py
@@ -0,0 +1,6 @@
+from email.headerregistry import Address
+from email.message import EmailMessage
+
+msg = EmailMessage()
+msg["To"] = "receiver@example.com"
+msg["From"] = Address("Sender Name", "sender", "example.com")
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/itertools/check_itertools_recipes.py b/mypy/typeshed/stdlib/@tests/test_cases/itertools/check_itertools_recipes.py
new file mode 100644
index 000000000000..c45ffee28cee
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/itertools/check_itertools_recipes.py
@@ -0,0 +1,410 @@
+"""Type-annotated versions of the recipes from the itertools docs.
+
+These are all meant to be examples of idiomatic itertools usage,
+so they should all type-check without error.
+"""
+
+from __future__ import annotations
+
+import collections
+import math
+import operator
+import sys
+from itertools import chain, combinations, count, cycle, filterfalse, groupby, islice, product, repeat, starmap, tee, zip_longest
+from typing import (
+    Any,
+    Callable,
+    Collection,
+    Hashable,
+    Iterable,
+    Iterator,
+    Literal,
+    Sequence,
+    Tuple,
+    Type,
+    TypeVar,
+    Union,
+    overload,
+)
+from typing_extensions import TypeAlias, TypeVarTuple, Unpack
+
+_T = TypeVar("_T")
+_T1 = TypeVar("_T1")
+_T2 = TypeVar("_T2")
+_HashableT = TypeVar("_HashableT", bound=Hashable)
+_Ts = TypeVarTuple("_Ts")
+
+
+def take(n: int, iterable: Iterable[_T]) -> list[_T]:
+    "Return first n items of the iterable as a list"
+    return list(islice(iterable, n))
+
+
+# Note: the itertools docs uses the parameter name "iterator",
+# but the function actually accepts any iterable
+# as its second argument
+def prepend(value: _T1, iterator: Iterable[_T2]) -> Iterator[_T1 | _T2]:
+    "Prepend a single value in front of an iterator"
+    # prepend(1, [2, 3, 4]) --> 1 2 3 4
+    return chain([value], iterator)
+
+
+def tabulate(function: Callable[[int], _T], start: int = 0) -> Iterator[_T]:
+    "Return function(0), function(1), ..."
+    return map(function, count(start))
+
+
+def repeatfunc(func: Callable[[Unpack[_Ts]], _T], times: int | None = None, *args: Unpack[_Ts]) -> Iterator[_T]:
+    """Repeat calls to func with specified arguments.
+
+    Example:  repeatfunc(random.random)
+    """
+    if times is None:
+        return starmap(func, repeat(args))
+    return starmap(func, repeat(args, times))
+
+
+def flatten(list_of_lists: Iterable[Iterable[_T]]) -> Iterator[_T]:
+    "Flatten one level of nesting"
+    return chain.from_iterable(list_of_lists)
+
+
+def ncycles(iterable: Iterable[_T], n: int) -> Iterator[_T]:
+    "Returns the sequence elements n times"
+    return chain.from_iterable(repeat(tuple(iterable), n))
+
+
+def tail(n: int, iterable: Iterable[_T]) -> Iterator[_T]:
+    "Return an iterator over the last n items"
+    # tail(3, 'ABCDEFG') --> E F G
+    return iter(collections.deque(iterable, maxlen=n))
+
+
+# This function *accepts* any iterable,
+# but it only *makes sense* to use it with an iterator
+def consume(iterator: Iterator[object], n: int | None = None) -> None:
+    "Advance the iterator n-steps ahead. If n is None, consume entirely."
+    # Use functions that consume iterators at C speed.
+    if n is None:
+        # feed the entire iterator into a zero-length deque
+        collections.deque(iterator, maxlen=0)
+    else:
+        # advance to the empty slice starting at position n
+        next(islice(iterator, n, n), None)
+
+
+@overload
+def nth(iterable: Iterable[_T], n: int, default: None = None) -> _T | None: ...
+
+
+@overload
+def nth(iterable: Iterable[_T], n: int, default: _T1) -> _T | _T1: ...
+
+
+def nth(iterable: Iterable[object], n: int, default: object = None) -> object:
+    "Returns the nth item or a default value"
+    return next(islice(iterable, n, None), default)
+
+
+@overload
+def quantify(iterable: Iterable[object]) -> int: ...
+
+
+@overload
+def quantify(iterable: Iterable[_T], pred: Callable[[_T], bool]) -> int: ...
+
+
+def quantify(iterable: Iterable[object], pred: Callable[[Any], bool] = bool) -> int:
+    "Given a predicate that returns True or False, count the True results."
+    return sum(map(pred, iterable))
+
+
+@overload
+def first_true(
+    iterable: Iterable[_T], default: Literal[False] = False, pred: Callable[[_T], bool] | None = None
+) -> _T | Literal[False]: ...
+
+
+@overload
+def first_true(iterable: Iterable[_T], default: _T1, pred: Callable[[_T], bool] | None = None) -> _T | _T1: ...
+
+
+def first_true(iterable: Iterable[object], default: object = False, pred: Callable[[Any], bool] | None = None) -> object:
+    """Returns the first true value in the iterable.
+    If no true value is found, returns *default*
+    If *pred* is not None, returns the first item
+    for which pred(item) is true.
+    """
+    # first_true([a,b,c], x) --> a or b or c or x
+    # first_true([a,b], x, f) --> a if f(a) else b if f(b) else x
+    return next(filter(pred, iterable), default)
+
+
+_ExceptionOrExceptionTuple: TypeAlias = Union[Type[BaseException], Tuple[Type[BaseException], ...]]
+
+
+@overload
+def iter_except(func: Callable[[], _T], exception: _ExceptionOrExceptionTuple, first: None = None) -> Iterator[_T]: ...
+
+
+@overload
+def iter_except(
+    func: Callable[[], _T], exception: _ExceptionOrExceptionTuple, first: Callable[[], _T1]
+) -> Iterator[_T | _T1]: ...
+
+
+def iter_except(
+    func: Callable[[], object], exception: _ExceptionOrExceptionTuple, first: Callable[[], object] | None = None
+) -> Iterator[object]:
+    """Call a function repeatedly until an exception is raised.
+    Converts a call-until-exception interface to an iterator interface.
+    Like builtins.iter(func, sentinel) but uses an exception instead
+    of a sentinel to end the loop.
+    Examples:
+        iter_except(functools.partial(heappop, h), IndexError)   # priority queue iterator
+        iter_except(d.popitem, KeyError)                         # non-blocking dict iterator
+        iter_except(d.popleft, IndexError)                       # non-blocking deque iterator
+        iter_except(q.get_nowait, Queue.Empty)                   # loop over a producer Queue
+        iter_except(s.pop, KeyError)                             # non-blocking set iterator
+    """
+    try:
+        if first is not None:
+            yield first()  # For database APIs needing an initial cast to db.first()
+        while True:
+            yield func()
+    except exception:
+        pass
+
+
+def sliding_window(iterable: Iterable[_T], n: int) -> Iterator[tuple[_T, ...]]:
+    # sliding_window('ABCDEFG', 4) --> ABCD BCDE CDEF DEFG
+    it = iter(iterable)
+    window = collections.deque(islice(it, n - 1), maxlen=n)
+    for x in it:
+        window.append(x)
+        yield tuple(window)
+
+
+def roundrobin(*iterables: Iterable[_T]) -> Iterator[_T]:
+    "roundrobin('ABC', 'D', 'EF') --> A D E B F C"
+    # Recipe credited to George Sakkis
+    num_active = len(iterables)
+    nexts: Iterator[Callable[[], _T]] = cycle(iter(it).__next__ for it in iterables)
+    while num_active:
+        try:
+            for next in nexts:
+                yield next()
+        except StopIteration:
+            # Remove the iterator we just exhausted from the cycle.
+            num_active -= 1
+            nexts = cycle(islice(nexts, num_active))
+
+
+def partition(pred: Callable[[_T], bool], iterable: Iterable[_T]) -> tuple[Iterator[_T], Iterator[_T]]:
+    """Partition entries into false entries and true entries.
+    If *pred* is slow, consider wrapping it with functools.lru_cache().
+    """
+    # partition(is_odd, range(10)) --> 0 2 4 6 8   and  1 3 5 7 9
+    t1, t2 = tee(iterable)
+    return filterfalse(pred, t1), filter(pred, t2)
+
+
+def subslices(seq: Sequence[_T]) -> Iterator[Sequence[_T]]:
+    "Return all contiguous non-empty subslices of a sequence"
+    # subslices('ABCD') --> A AB ABC ABCD B BC BCD C CD D
+    slices = starmap(slice, combinations(range(len(seq) + 1), 2))
+    return map(operator.getitem, repeat(seq), slices)
+
+
+def before_and_after(predicate: Callable[[_T], bool], it: Iterable[_T]) -> tuple[Iterator[_T], Iterator[_T]]:
+    """Variant of takewhile() that allows complete
+    access to the remainder of the iterator.
+    >>> it = iter('ABCdEfGhI')
+    >>> all_upper, remainder = before_and_after(str.isupper, it)
+    >>> ''.join(all_upper)
+    'ABC'
+    >>> ''.join(remainder)     # takewhile() would lose the 'd'
+    'dEfGhI'
+    Note that the first iterator must be fully
+    consumed before the second iterator can
+    generate valid results.
+    """
+    it = iter(it)
+    transition: list[_T] = []
+
+    def true_iterator() -> Iterator[_T]:
+        for elem in it:
+            if predicate(elem):
+                yield elem
+            else:
+                transition.append(elem)
+                return
+
+    def remainder_iterator() -> Iterator[_T]:
+        yield from transition
+        yield from it
+
+    return true_iterator(), remainder_iterator()
+
+
+@overload
+def unique_everseen(iterable: Iterable[_HashableT], key: None = None) -> Iterator[_HashableT]: ...
+
+
+@overload
+def unique_everseen(iterable: Iterable[_T], key: Callable[[_T], Hashable]) -> Iterator[_T]: ...
+
+
+def unique_everseen(iterable: Iterable[_T], key: Callable[[_T], Hashable] | None = None) -> Iterator[_T]:
+    "List unique elements, preserving order. Remember all elements ever seen."
+    # unique_everseen('AAAABBBCCDAABBB') --> A B C D
+    # unique_everseen('ABBcCAD', str.lower) --> A B c D
+    seen: set[Hashable] = set()
+    if key is None:
+        for element in filterfalse(seen.__contains__, iterable):
+            seen.add(element)
+            yield element
+        # For order preserving deduplication,
+        # a faster but non-lazy solution is:
+        #     yield from dict.fromkeys(iterable)
+    else:
+        for element in iterable:
+            k = key(element)
+            if k not in seen:
+                seen.add(k)
+                yield element
+        # For use cases that allow the last matching element to be returned,
+        # a faster but non-lazy solution is:
+        #      t1, t2 = tee(iterable)
+        #      yield from dict(zip(map(key, t1), t2)).values()
+
+
+# Slightly adapted from the docs recipe; a one-liner was a bit much for pyright
+def unique_justseen(iterable: Iterable[_T], key: Callable[[_T], bool] | None = None) -> Iterator[_T]:
+    "List unique elements, preserving order. Remember only the element just seen."
+    # unique_justseen('AAAABBBCCDAABBB') --> A B C D A B
+    # unique_justseen('ABBcCAD', str.lower) --> A B c A D
+    g: groupby[_T | bool, _T] = groupby(iterable, key)
+    return map(next, map(operator.itemgetter(1), g))
+
+
+def powerset(iterable: Iterable[_T]) -> Iterator[tuple[_T, ...]]:
+    "powerset([1,2,3]) --> () (1,) (2,) (3,) (1,2) (1,3) (2,3) (1,2,3)"
+    s = list(iterable)
+    return chain.from_iterable(combinations(s, r) for r in range(len(s) + 1))
+
+
+def polynomial_derivative(coefficients: Sequence[float]) -> list[float]:
+    """Compute the first derivative of a polynomial.
+    f(x)  =  x³ -4x² -17x + 60
+    f'(x) = 3x² -8x  -17
+    """
+    # polynomial_derivative([1, -4, -17, 60]) -> [3, -8, -17]
+    n = len(coefficients)
+    powers = reversed(range(1, n))
+    return list(map(operator.mul, coefficients, powers))
+
+
+def nth_combination(iterable: Iterable[_T], r: int, index: int) -> tuple[_T, ...]:
+    "Equivalent to list(combinations(iterable, r))[index]"
+    pool = tuple(iterable)
+    n = len(pool)
+    c = math.comb(n, r)
+    if index < 0:
+        index += c
+    if index < 0 or index >= c:
+        raise IndexError
+    result: list[_T] = []
+    while r:
+        c, n, r = c * r // n, n - 1, r - 1
+        while index >= c:
+            index -= c
+            c, n = c * (n - r) // n, n - 1
+        result.append(pool[-1 - n])
+    return tuple(result)
+
+
+if sys.version_info >= (3, 10):
+
+    @overload
+    def grouper(
+        iterable: Iterable[_T], n: int, *, incomplete: Literal["fill"] = "fill", fillvalue: None = None
+    ) -> Iterator[tuple[_T | None, ...]]: ...
+
+    @overload
+    def grouper(
+        iterable: Iterable[_T], n: int, *, incomplete: Literal["fill"] = "fill", fillvalue: _T1
+    ) -> Iterator[tuple[_T | _T1, ...]]: ...
+
+    @overload
+    def grouper(
+        iterable: Iterable[_T], n: int, *, incomplete: Literal["strict", "ignore"], fillvalue: None = None
+    ) -> Iterator[tuple[_T, ...]]: ...
+
+    def grouper(
+        iterable: Iterable[object], n: int, *, incomplete: Literal["fill", "strict", "ignore"] = "fill", fillvalue: object = None
+    ) -> Iterator[tuple[object, ...]]:
+        "Collect data into non-overlapping fixed-length chunks or blocks"
+        # grouper('ABCDEFG', 3, fillvalue='x') --> ABC DEF Gxx
+        # grouper('ABCDEFG', 3, incomplete='strict') --> ABC DEF ValueError
+        # grouper('ABCDEFG', 3, incomplete='ignore') --> ABC DEF
+        args = [iter(iterable)] * n
+        if incomplete == "fill":
+            return zip_longest(*args, fillvalue=fillvalue)
+        if incomplete == "strict":
+            return zip(*args, strict=True)
+        if incomplete == "ignore":
+            return zip(*args)
+        else:
+            raise ValueError("Expected fill, strict, or ignore")
+
+    def transpose(it: Iterable[Iterable[_T]]) -> Iterator[tuple[_T, ...]]:
+        "Swap the rows and columns of the input."
+        # transpose([(1, 2, 3), (11, 22, 33)]) --> (1, 11) (2, 22) (3, 33)
+        return zip(*it, strict=True)
+
+
+if sys.version_info >= (3, 12):
+    from itertools import batched
+
+    def sum_of_squares(it: Iterable[float]) -> float:
+        "Add up the squares of the input values."
+        # sum_of_squares([10, 20, 30]) -> 1400
+        return math.sumprod(*tee(it))
+
+    def convolve(signal: Iterable[float], kernel: Iterable[float]) -> Iterator[float]:
+        """Discrete linear convolution of two iterables.
+        The kernel is fully consumed before the calculations begin.
+        The signal is consumed lazily and can be infinite.
+        Convolutions are mathematically commutative.
+        If the signal and kernel are swapped,
+        the output will be the same.
+        Article:  https://betterexplained.com/articles/intuitive-convolution/
+        Video:    https://www.youtube.com/watch?v=KuXjwB4LzSA
+        """
+        # convolve(data, [0.25, 0.25, 0.25, 0.25]) --> Moving average (blur)
+        # convolve(data, [1/2, 0, -1/2]) --> 1st derivative estimate
+        # convolve(data, [1, -2, 1]) --> 2nd derivative estimate
+        kernel = tuple(kernel)[::-1]
+        n = len(kernel)
+        padded_signal = chain(repeat(0, n - 1), signal, repeat(0, n - 1))
+        windowed_signal = sliding_window(padded_signal, n)
+        return map(math.sumprod, repeat(kernel), windowed_signal)
+
+    def polynomial_eval(coefficients: Sequence[float], x: float) -> float:
+        """Evaluate a polynomial at a specific value.
+        Computes with better numeric stability than Horner's method.
+        """
+        # Evaluate x³ -4x² -17x + 60 at x = 2.5
+        # polynomial_eval([1, -4, -17, 60], x=2.5) --> 8.125
+        n = len(coefficients)
+        if not n:
+            return type(x)(0)
+        powers = map(pow, repeat(x), reversed(range(n)))
+        return math.sumprod(coefficients, powers)
+
+    def matmul(m1: Sequence[Collection[float]], m2: Sequence[Collection[float]]) -> Iterator[tuple[float, ...]]:
+        "Multiply two matrices."
+        # matmul([(7, 5), (3, 5)], [(2, 5), (7, 9)]) --> (49, 80), (41, 60)
+        n = len(m2[0])
+        return batched(starmap(math.sumprod, product(m1, transpose(m2))), n)
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/typing/check_MutableMapping.py b/mypy/typeshed/stdlib/@tests/test_cases/typing/check_MutableMapping.py
new file mode 100644
index 000000000000..10a33ffb83d5
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/typing/check_MutableMapping.py
@@ -0,0 +1,18 @@
+from __future__ import annotations
+
+from typing import Any, Union
+from typing_extensions import assert_type
+
+
+def check_setdefault_method() -> None:
+    d: dict[int, str] = {}
+    d2: dict[int, str | None] = {}
+    d3: dict[int, Any] = {}
+
+    d.setdefault(1)  # type: ignore
+    assert_type(d.setdefault(1, "x"), str)
+    assert_type(d2.setdefault(1), Union[str, None])
+    assert_type(d2.setdefault(1, None), Union[str, None])
+    assert_type(d2.setdefault(1, "x"), Union[str, None])
+    assert_type(d3.setdefault(1), Union[Any, None])
+    assert_type(d3.setdefault(1, "x"), Any)
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/typing/check_all.py b/mypy/typeshed/stdlib/@tests/test_cases/typing/check_all.py
new file mode 100644
index 000000000000..44eb548e04a9
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/typing/check_all.py
@@ -0,0 +1,14 @@
+# pyright: reportWildcardImportFromLibrary=false
+"""
+This tests that star imports work when using "all += " syntax.
+"""
+from __future__ import annotations
+
+import sys
+from typing import *
+from zipfile import *
+
+if sys.version_info >= (3, 9):
+    x: Annotated[int, 42]
+
+p: Path
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/typing/check_regression_issue_9296.py b/mypy/typeshed/stdlib/@tests/test_cases/typing/check_regression_issue_9296.py
new file mode 100644
index 000000000000..34c5631aeb1a
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/typing/check_regression_issue_9296.py
@@ -0,0 +1,16 @@
+from __future__ import annotations
+
+import typing as t
+
+KT = t.TypeVar("KT")
+
+
+class MyKeysView(t.KeysView[KT]):
+    pass
+
+
+d: dict[t.Any, t.Any] = {}
+dict_keys = type(d.keys())
+
+# This should not cause an error like `Member "register" is unknown`:
+MyKeysView.register(dict_keys)
diff --git a/mypy/typeshed/stdlib/@tests/test_cases/typing/check_typing_io.py b/mypy/typeshed/stdlib/@tests/test_cases/typing/check_typing_io.py
new file mode 100644
index 000000000000..67f16dc91765
--- /dev/null
+++ b/mypy/typeshed/stdlib/@tests/test_cases/typing/check_typing_io.py
@@ -0,0 +1,21 @@
+from __future__ import annotations
+
+import mmap
+from typing import IO, AnyStr
+
+
+def check_write(io_bytes: IO[bytes], io_str: IO[str], io_anystr: IO[AnyStr], any_str: AnyStr, buf: mmap.mmap) -> None:
+    io_bytes.write(b"")
+    io_bytes.write(buf)
+    io_bytes.write("")  # type: ignore
+    io_bytes.write(any_str)  # type: ignore
+
+    io_str.write(b"")  # type: ignore
+    io_str.write(buf)  # type: ignore
+    io_str.write("")
+    io_str.write(any_str)  # type: ignore
+
+    io_anystr.write(b"")  # type: ignore
+    io_anystr.write(buf)  # type: ignore
+    io_anystr.write("")  # type: ignore
+    io_anystr.write(any_str)
diff --git a/mypy/typeshed/stdlib/_typeshed/importlib.pyi b/mypy/typeshed/stdlib/_typeshed/importlib.pyi
new file mode 100644
index 000000000000..a4e56cdaff62
--- /dev/null
+++ b/mypy/typeshed/stdlib/_typeshed/importlib.pyi
@@ -0,0 +1,18 @@
+# Implicit protocols used in importlib.
+# We intentionally omit deprecated and optional methods.
+
+from collections.abc import Sequence
+from importlib.machinery import ModuleSpec
+from types import ModuleType
+from typing import Protocol
+
+__all__ = ["LoaderProtocol", "MetaPathFinderProtocol", "PathEntryFinderProtocol"]
+
+class LoaderProtocol(Protocol):
+    def load_module(self, fullname: str, /) -> ModuleType: ...
+
+class MetaPathFinderProtocol(Protocol):
+    def find_spec(self, fullname: str, path: Sequence[str] | None, target: ModuleType | None = ..., /) -> ModuleSpec | None: ...
+
+class PathEntryFinderProtocol(Protocol):
+    def find_spec(self, fullname: str, target: ModuleType | None = ..., /) -> ModuleSpec | None: ...
diff --git a/mypy/typeshed/stdlib/ast.pyi b/mypy/typeshed/stdlib/ast.pyi
index 4ab325b5baa7..2525c3642a6f 100644
--- a/mypy/typeshed/stdlib/ast.pyi
+++ b/mypy/typeshed/stdlib/ast.pyi
@@ -181,82 +181,172 @@ class NodeTransformer(NodeVisitor):
 
 _T = _TypeVar("_T", bound=AST)
 
-@overload
-def parse(
-    source: str | ReadableBuffer,
-    filename: str | ReadableBuffer | os.PathLike[Any] = "<unknown>",
-    mode: Literal["exec"] = "exec",
-    *,
-    type_comments: bool = False,
-    feature_version: None | int | tuple[int, int] = None,
-) -> Module: ...
-@overload
-def parse(
-    source: str | ReadableBuffer,
-    filename: str | ReadableBuffer | os.PathLike[Any],
-    mode: Literal["eval"],
-    *,
-    type_comments: bool = False,
-    feature_version: None | int | tuple[int, int] = None,
-) -> Expression: ...
-@overload
-def parse(
-    source: str | ReadableBuffer,
-    filename: str | ReadableBuffer | os.PathLike[Any],
-    mode: Literal["func_type"],
-    *,
-    type_comments: bool = False,
-    feature_version: None | int | tuple[int, int] = None,
-) -> FunctionType: ...
-@overload
-def parse(
-    source: str | ReadableBuffer,
-    filename: str | ReadableBuffer | os.PathLike[Any],
-    mode: Literal["single"],
-    *,
-    type_comments: bool = False,
-    feature_version: None | int | tuple[int, int] = None,
-) -> Interactive: ...
-@overload
-def parse(
-    source: str | ReadableBuffer,
-    *,
-    mode: Literal["eval"],
-    type_comments: bool = False,
-    feature_version: None | int | tuple[int, int] = None,
-) -> Expression: ...
-@overload
-def parse(
-    source: str | ReadableBuffer,
-    *,
-    mode: Literal["func_type"],
-    type_comments: bool = False,
-    feature_version: None | int | tuple[int, int] = None,
-) -> FunctionType: ...
-@overload
-def parse(
-    source: str | ReadableBuffer,
-    *,
-    mode: Literal["single"],
-    type_comments: bool = False,
-    feature_version: None | int | tuple[int, int] = None,
-) -> Interactive: ...
-@overload
-def parse(
-    source: str | ReadableBuffer,
-    filename: str | ReadableBuffer | os.PathLike[Any] = "<unknown>",
-    mode: str = "exec",
-    *,
-    type_comments: bool = False,
-    feature_version: None | int | tuple[int, int] = None,
-) -> AST: ...
+if sys.version_info >= (3, 13):
+    @overload
+    def parse(
+        source: str | ReadableBuffer,
+        filename: str | ReadableBuffer | os.PathLike[Any] = "<unknown>",
+        mode: Literal["exec"] = "exec",
+        *,
+        type_comments: bool = False,
+        feature_version: None | int | tuple[int, int] = None,
+        optimize: Literal[-1, 0, 1, 2] = -1,
+    ) -> Module: ...
+    @overload
+    def parse(
+        source: str | ReadableBuffer,
+        filename: str | ReadableBuffer | os.PathLike[Any],
+        mode: Literal["eval"],
+        *,
+        type_comments: bool = False,
+        feature_version: None | int | tuple[int, int] = None,
+        optimize: Literal[-1, 0, 1, 2] = -1,
+    ) -> Expression: ...
+    @overload
+    def parse(
+        source: str | ReadableBuffer,
+        filename: str | ReadableBuffer | os.PathLike[Any],
+        mode: Literal["func_type"],
+        *,
+        type_comments: bool = False,
+        feature_version: None | int | tuple[int, int] = None,
+        optimize: Literal[-1, 0, 1, 2] = -1,
+    ) -> FunctionType: ...
+    @overload
+    def parse(
+        source: str | ReadableBuffer,
+        filename: str | ReadableBuffer | os.PathLike[Any],
+        mode: Literal["single"],
+        *,
+        type_comments: bool = False,
+        feature_version: None | int | tuple[int, int] = None,
+        optimize: Literal[-1, 0, 1, 2] = -1,
+    ) -> Interactive: ...
+    @overload
+    def parse(
+        source: str | ReadableBuffer,
+        *,
+        mode: Literal["eval"],
+        type_comments: bool = False,
+        feature_version: None | int | tuple[int, int] = None,
+        optimize: Literal[-1, 0, 1, 2] = -1,
+    ) -> Expression: ...
+    @overload
+    def parse(
+        source: str | ReadableBuffer,
+        *,
+        mode: Literal["func_type"],
+        type_comments: bool = False,
+        feature_version: None | int | tuple[int, int] = None,
+        optimize: Literal[-1, 0, 1, 2] = -1,
+    ) -> FunctionType: ...
+    @overload
+    def parse(
+        source: str | ReadableBuffer,
+        *,
+        mode: Literal["single"],
+        type_comments: bool = False,
+        feature_version: None | int | tuple[int, int] = None,
+        optimize: Literal[-1, 0, 1, 2] = -1,
+    ) -> Interactive: ...
+    @overload
+    def parse(
+        source: str | ReadableBuffer,
+        filename: str | ReadableBuffer | os.PathLike[Any] = "<unknown>",
+        mode: str = "exec",
+        *,
+        type_comments: bool = False,
+        feature_version: None | int | tuple[int, int] = None,
+        optimize: Literal[-1, 0, 1, 2] = -1,
+    ) -> AST: ...
+
+else:
+    @overload
+    def parse(
+        source: str | ReadableBuffer,
+        filename: str | ReadableBuffer | os.PathLike[Any] = "<unknown>",
+        mode: Literal["exec"] = "exec",
+        *,
+        type_comments: bool = False,
+        feature_version: None | int | tuple[int, int] = None,
+    ) -> Module: ...
+    @overload
+    def parse(
+        source: str | ReadableBuffer,
+        filename: str | ReadableBuffer | os.PathLike[Any],
+        mode: Literal["eval"],
+        *,
+        type_comments: bool = False,
+        feature_version: None | int | tuple[int, int] = None,
+    ) -> Expression: ...
+    @overload
+    def parse(
+        source: str | ReadableBuffer,
+        filename: str | ReadableBuffer | os.PathLike[Any],
+        mode: Literal["func_type"],
+        *,
+        type_comments: bool = False,
+        feature_version: None | int | tuple[int, int] = None,
+    ) -> FunctionType: ...
+    @overload
+    def parse(
+        source: str | ReadableBuffer,
+        filename: str | ReadableBuffer | os.PathLike[Any],
+        mode: Literal["single"],
+        *,
+        type_comments: bool = False,
+        feature_version: None | int | tuple[int, int] = None,
+    ) -> Interactive: ...
+    @overload
+    def parse(
+        source: str | ReadableBuffer,
+        *,
+        mode: Literal["eval"],
+        type_comments: bool = False,
+        feature_version: None | int | tuple[int, int] = None,
+    ) -> Expression: ...
+    @overload
+    def parse(
+        source: str | ReadableBuffer,
+        *,
+        mode: Literal["func_type"],
+        type_comments: bool = False,
+        feature_version: None | int | tuple[int, int] = None,
+    ) -> FunctionType: ...
+    @overload
+    def parse(
+        source: str | ReadableBuffer,
+        *,
+        mode: Literal["single"],
+        type_comments: bool = False,
+        feature_version: None | int | tuple[int, int] = None,
+    ) -> Interactive: ...
+    @overload
+    def parse(
+        source: str | ReadableBuffer,
+        filename: str | ReadableBuffer | os.PathLike[Any] = "<unknown>",
+        mode: str = "exec",
+        *,
+        type_comments: bool = False,
+        feature_version: None | int | tuple[int, int] = None,
+    ) -> AST: ...
 
 if sys.version_info >= (3, 9):
     def unparse(ast_obj: AST) -> str: ...
 
 def copy_location(new_node: _T, old_node: AST) -> _T: ...
 
-if sys.version_info >= (3, 9):
+if sys.version_info >= (3, 13):
+    def dump(
+        node: AST,
+        annotate_fields: bool = True,
+        include_attributes: bool = False,
+        *,
+        indent: int | str | None = None,
+        show_empty: bool = False,
+    ) -> str: ...
+
+elif sys.version_info >= (3, 9):
     def dump(
         node: AST, annotate_fields: bool = True, include_attributes: bool = False, *, indent: int | str | None = None
     ) -> str: ...
diff --git a/mypy/typeshed/stdlib/builtins.pyi b/mypy/typeshed/stdlib/builtins.pyi
index 9e56c5430c52..4c47a0736e2e 100644
--- a/mypy/typeshed/stdlib/builtins.pyi
+++ b/mypy/typeshed/stdlib/builtins.pyi
@@ -31,7 +31,7 @@ from _typeshed import (
 )
 from collections.abc import Awaitable, Callable, Iterable, Iterator, MutableSet, Reversible, Set as AbstractSet, Sized
 from io import BufferedRandom, BufferedReader, BufferedWriter, FileIO, TextIOWrapper
-from types import CodeType, TracebackType, _Cell
+from types import CellType, CodeType, TracebackType
 
 # mypy crashes if any of {ByteString, Sequence, MutableSequence, Mapping, MutableMapping} are imported from collections.abc in builtins.pyi
 from typing import (  # noqa: Y022
@@ -863,7 +863,7 @@ class tuple(Sequence[_T_co]):
 class function:
     # Make sure this class definition stays roughly in line with `types.FunctionType`
     @property
-    def __closure__(self) -> tuple[_Cell, ...] | None: ...
+    def __closure__(self) -> tuple[CellType, ...] | None: ...
     __code__: CodeType
     __defaults__: tuple[Any, ...] | None
     __dict__: dict[str, Any]
@@ -1245,7 +1245,7 @@ if sys.version_info >= (3, 11):
         locals: Mapping[str, object] | None = None,
         /,
         *,
-        closure: tuple[_Cell, ...] | None = None,
+        closure: tuple[CellType, ...] | None = None,
     ) -> None: ...
 
 else:
@@ -1706,7 +1706,7 @@ def __import__(
     fromlist: Sequence[str] = (),
     level: int = 0,
 ) -> types.ModuleType: ...
-def __build_class__(func: Callable[[], _Cell | Any], name: str, /, *bases: Any, metaclass: Any = ..., **kwds: Any) -> Any: ...
+def __build_class__(func: Callable[[], CellType | Any], name: str, /, *bases: Any, metaclass: Any = ..., **kwds: Any) -> Any: ...
 
 if sys.version_info >= (3, 10):
     from types import EllipsisType
diff --git a/mypy/typeshed/stdlib/dbm/__init__.pyi b/mypy/typeshed/stdlib/dbm/__init__.pyi
index 9c6989a1c151..f414763e02a6 100644
--- a/mypy/typeshed/stdlib/dbm/__init__.pyi
+++ b/mypy/typeshed/stdlib/dbm/__init__.pyi
@@ -1,3 +1,5 @@
+import sys
+from _typeshed import StrOrBytesPath
 from collections.abc import Iterator, MutableMapping
 from types import TracebackType
 from typing import Literal
@@ -91,5 +93,10 @@ class _error(Exception): ...
 
 error: tuple[type[_error], type[OSError]]
 
-def whichdb(filename: str) -> str | None: ...
-def open(file: str, flag: _TFlags = "r", mode: int = 0o666) -> _Database: ...
+if sys.version_info >= (3, 11):
+    def whichdb(filename: StrOrBytesPath) -> str | None: ...
+    def open(file: StrOrBytesPath, flag: _TFlags = "r", mode: int = 0o666) -> _Database: ...
+
+else:
+    def whichdb(filename: str) -> str | None: ...
+    def open(file: str, flag: _TFlags = "r", mode: int = 0o666) -> _Database: ...
diff --git a/mypy/typeshed/stdlib/dbm/dumb.pyi b/mypy/typeshed/stdlib/dbm/dumb.pyi
index 1fc68cf71f9d..1c0b7756f292 100644
--- a/mypy/typeshed/stdlib/dbm/dumb.pyi
+++ b/mypy/typeshed/stdlib/dbm/dumb.pyi
@@ -1,3 +1,5 @@
+import sys
+from _typeshed import StrOrBytesPath
 from collections.abc import Iterator, MutableMapping
 from types import TracebackType
 from typing_extensions import Self, TypeAlias
@@ -28,4 +30,8 @@ class _Database(MutableMapping[_KeyType, bytes]):
         self, exc_type: type[BaseException] | None, exc_val: BaseException | None, exc_tb: TracebackType | None
     ) -> None: ...
 
-def open(file: str, flag: str = "c", mode: int = 0o666) -> _Database: ...
+if sys.version_info >= (3, 11):
+    def open(file: StrOrBytesPath, flag: str = "c", mode: int = 0o666) -> _Database: ...
+
+else:
+    def open(file: str, flag: str = "c", mode: int = 0o666) -> _Database: ...
diff --git a/mypy/typeshed/stdlib/dbm/gnu.pyi b/mypy/typeshed/stdlib/dbm/gnu.pyi
index 8b562019fcfb..e80441cbb25b 100644
--- a/mypy/typeshed/stdlib/dbm/gnu.pyi
+++ b/mypy/typeshed/stdlib/dbm/gnu.pyi
@@ -1,5 +1,5 @@
 import sys
-from _typeshed import ReadOnlyBuffer
+from _typeshed import ReadOnlyBuffer, StrOrBytesPath
 from types import TracebackType
 from typing import TypeVar, overload
 from typing_extensions import Self, TypeAlias
@@ -38,4 +38,7 @@ if sys.platform != "win32":
         __new__: None  # type: ignore[assignment]
         __init__: None  # type: ignore[assignment]
 
-    def open(filename: str, flags: str = "r", mode: int = 0o666, /) -> _gdbm: ...
+    if sys.version_info >= (3, 11):
+        def open(filename: StrOrBytesPath, flags: str = "r", mode: int = 0o666, /) -> _gdbm: ...
+    else:
+        def open(filename: str, flags: str = "r", mode: int = 0o666, /) -> _gdbm: ...
diff --git a/mypy/typeshed/stdlib/dbm/ndbm.pyi b/mypy/typeshed/stdlib/dbm/ndbm.pyi
index 5eb84e6949fc..02bf23ec181c 100644
--- a/mypy/typeshed/stdlib/dbm/ndbm.pyi
+++ b/mypy/typeshed/stdlib/dbm/ndbm.pyi
@@ -1,5 +1,5 @@
 import sys
-from _typeshed import ReadOnlyBuffer
+from _typeshed import ReadOnlyBuffer, StrOrBytesPath
 from types import TracebackType
 from typing import TypeVar, overload
 from typing_extensions import Self, TypeAlias
@@ -34,4 +34,7 @@ if sys.platform != "win32":
         __new__: None  # type: ignore[assignment]
         __init__: None  # type: ignore[assignment]
 
-    def open(filename: str, flags: str = "r", mode: int = 0o666, /) -> _dbm: ...
+    if sys.version_info >= (3, 11):
+        def open(filename: StrOrBytesPath, flags: str = "r", mode: int = 0o666, /) -> _dbm: ...
+    else:
+        def open(filename: str, flags: str = "r", mode: int = 0o666, /) -> _dbm: ...
diff --git a/mypy/typeshed/stdlib/importlib/abc.pyi b/mypy/typeshed/stdlib/importlib/abc.pyi
index 75e78ed59172..3937481159dc 100644
--- a/mypy/typeshed/stdlib/importlib/abc.pyi
+++ b/mypy/typeshed/stdlib/importlib/abc.pyi
@@ -64,7 +64,7 @@ class SourceLoader(ResourceLoader, ExecutionLoader, metaclass=ABCMeta):
 
 # The base classes differ starting in 3.10:
 if sys.version_info >= (3, 10):
-    # Please keep in sync with sys._MetaPathFinder
+    # Please keep in sync with _typeshed.importlib.MetaPathFinderProtocol
     class MetaPathFinder(metaclass=ABCMeta):
         if sys.version_info < (3, 12):
             def find_module(self, fullname: str, path: Sequence[str] | None) -> Loader | None: ...
@@ -85,7 +85,7 @@ if sys.version_info >= (3, 10):
         def find_spec(self, fullname: str, target: types.ModuleType | None = ...) -> ModuleSpec | None: ...
 
 else:
-    # Please keep in sync with sys._MetaPathFinder
+    # Please keep in sync with _typeshed.importlib.MetaPathFinderProtocol
     class MetaPathFinder(Finder):
         def find_module(self, fullname: str, path: Sequence[str] | None) -> Loader | None: ...
         def invalidate_caches(self) -> None: ...
diff --git a/mypy/typeshed/stdlib/importlib/util.pyi b/mypy/typeshed/stdlib/importlib/util.pyi
index 6608f70d4469..2492c76d5c6c 100644
--- a/mypy/typeshed/stdlib/importlib/util.pyi
+++ b/mypy/typeshed/stdlib/importlib/util.pyi
@@ -3,6 +3,7 @@ import importlib.machinery
 import sys
 import types
 from _typeshed import ReadableBuffer, StrOrBytesPath
+from _typeshed.importlib import LoaderProtocol
 from collections.abc import Callable
 from typing import Any
 from typing_extensions import ParamSpec
@@ -23,13 +24,13 @@ def source_from_cache(path: str) -> str: ...
 def decode_source(source_bytes: ReadableBuffer) -> str: ...
 def find_spec(name: str, package: str | None = None) -> importlib.machinery.ModuleSpec | None: ...
 def spec_from_loader(
-    name: str, loader: importlib.abc.Loader | None, *, origin: str | None = None, is_package: bool | None = None
+    name: str, loader: LoaderProtocol | None, *, origin: str | None = None, is_package: bool | None = None
 ) -> importlib.machinery.ModuleSpec | None: ...
 def spec_from_file_location(
     name: str,
     location: StrOrBytesPath | None = None,
     *,
-    loader: importlib.abc.Loader | None = None,
+    loader: LoaderProtocol | None = None,
     submodule_search_locations: list[str] | None = ...,
 ) -> importlib.machinery.ModuleSpec | None: ...
 def module_from_spec(spec: importlib.machinery.ModuleSpec) -> types.ModuleType: ...
diff --git a/mypy/typeshed/stdlib/logging/__init__.pyi b/mypy/typeshed/stdlib/logging/__init__.pyi
index f5f7f91ece61..7ceddfa7ff28 100644
--- a/mypy/typeshed/stdlib/logging/__init__.pyi
+++ b/mypy/typeshed/stdlib/logging/__init__.pyi
@@ -587,7 +587,7 @@ def setLoggerClass(klass: type[Logger]) -> None: ...
 def captureWarnings(capture: bool) -> None: ...
 def setLogRecordFactory(factory: Callable[..., LogRecord]) -> None: ...
 
-lastResort: StreamHandler[Any] | None
+lastResort: Handler | None
 
 _StreamT = TypeVar("_StreamT", bound=SupportsWrite[str])
 
diff --git a/mypy/typeshed/stdlib/pathlib.pyi b/mypy/typeshed/stdlib/pathlib.pyi
index 5ea025095f68..0013e221f2e1 100644
--- a/mypy/typeshed/stdlib/pathlib.pyi
+++ b/mypy/typeshed/stdlib/pathlib.pyi
@@ -15,7 +15,7 @@ from io import BufferedRandom, BufferedReader, BufferedWriter, FileIO, TextIOWra
 from os import PathLike, stat_result
 from types import TracebackType
 from typing import IO, Any, BinaryIO, Literal, overload
-from typing_extensions import Self
+from typing_extensions import Self, deprecated
 
 if sys.version_info >= (3, 9):
     from types import GenericAlias
@@ -222,7 +222,11 @@ class Path(PurePath):
     else:
         def write_text(self, data: str, encoding: str | None = None, errors: str | None = None) -> int: ...
     if sys.version_info < (3, 12):
-        def link_to(self, target: StrOrBytesPath) -> None: ...
+        if sys.version_info >= (3, 10):
+            @deprecated("Deprecated as of Python 3.10 and removed in Python 3.12. Use hardlink_to() instead.")
+            def link_to(self, target: StrOrBytesPath) -> None: ...
+        else:
+            def link_to(self, target: StrOrBytesPath) -> None: ...
     if sys.version_info >= (3, 12):
         def walk(
             self, top_down: bool = ..., on_error: Callable[[OSError], object] | None = ..., follow_symlinks: bool = ...
diff --git a/mypy/typeshed/stdlib/pkgutil.pyi b/mypy/typeshed/stdlib/pkgutil.pyi
index 4a0c8d101b7a..7e7fa4fda9a1 100644
--- a/mypy/typeshed/stdlib/pkgutil.pyi
+++ b/mypy/typeshed/stdlib/pkgutil.pyi
@@ -1,7 +1,7 @@
 import sys
 from _typeshed import SupportsRead
+from _typeshed.importlib import LoaderProtocol, MetaPathFinderProtocol, PathEntryFinderProtocol
 from collections.abc import Callable, Iterable, Iterator
-from importlib.abc import Loader, MetaPathFinder, PathEntryFinder
 from typing import IO, Any, NamedTuple, TypeVar
 from typing_extensions import deprecated
 
@@ -23,7 +23,7 @@ if sys.version_info < (3, 12):
 _PathT = TypeVar("_PathT", bound=Iterable[str])
 
 class ModuleInfo(NamedTuple):
-    module_finder: MetaPathFinder | PathEntryFinder
+    module_finder: MetaPathFinderProtocol | PathEntryFinderProtocol
     name: str
     ispkg: bool
 
@@ -37,11 +37,11 @@ if sys.version_info < (3, 12):
         def __init__(self, fullname: str, file: IO[str], filename: str, etc: tuple[str, str, int]) -> None: ...
 
 @deprecated("Use importlib.util.find_spec() instead. Will be removed in Python 3.14.")
-def find_loader(fullname: str) -> Loader | None: ...
-def get_importer(path_item: str) -> PathEntryFinder | None: ...
+def find_loader(fullname: str) -> LoaderProtocol | None: ...
+def get_importer(path_item: str) -> PathEntryFinderProtocol | None: ...
 @deprecated("Use importlib.util.find_spec() instead. Will be removed in Python 3.14.")
-def get_loader(module_or_name: str) -> Loader | None: ...
-def iter_importers(fullname: str = "") -> Iterator[MetaPathFinder | PathEntryFinder]: ...
+def get_loader(module_or_name: str) -> LoaderProtocol | None: ...
+def iter_importers(fullname: str = "") -> Iterator[MetaPathFinderProtocol | PathEntryFinderProtocol]: ...
 def iter_modules(path: Iterable[str] | None = None, prefix: str = "") -> Iterator[ModuleInfo]: ...
 def read_code(stream: SupportsRead[bytes]) -> Any: ...  # undocumented
 def walk_packages(
diff --git a/mypy/typeshed/stdlib/shelve.pyi b/mypy/typeshed/stdlib/shelve.pyi
index 59abeafe6fca..654c2ea097f7 100644
--- a/mypy/typeshed/stdlib/shelve.pyi
+++ b/mypy/typeshed/stdlib/shelve.pyi
@@ -1,3 +1,5 @@
+import sys
+from _typeshed import StrOrBytesPath
 from collections.abc import Iterator, MutableMapping
 from dbm import _TFlags
 from types import TracebackType
@@ -41,6 +43,17 @@ class BsdDbShelf(Shelf[_VT]):
     def last(self) -> tuple[str, _VT]: ...
 
 class DbfilenameShelf(Shelf[_VT]):
-    def __init__(self, filename: str, flag: _TFlags = "c", protocol: int | None = None, writeback: bool = False) -> None: ...
+    if sys.version_info >= (3, 11):
+        def __init__(
+            self, filename: StrOrBytesPath, flag: _TFlags = "c", protocol: int | None = None, writeback: bool = False
+        ) -> None: ...
+    else:
+        def __init__(self, filename: str, flag: _TFlags = "c", protocol: int | None = None, writeback: bool = False) -> None: ...
 
-def open(filename: str, flag: _TFlags = "c", protocol: int | None = None, writeback: bool = False) -> Shelf[Any]: ...
+if sys.version_info >= (3, 11):
+    def open(
+        filename: StrOrBytesPath, flag: _TFlags = "c", protocol: int | None = None, writeback: bool = False
+    ) -> Shelf[Any]: ...
+
+else:
+    def open(filename: str, flag: _TFlags = "c", protocol: int | None = None, writeback: bool = False) -> Shelf[Any]: ...
diff --git a/mypy/typeshed/stdlib/socket.pyi b/mypy/typeshed/stdlib/socket.pyi
index a309bac9370a..b626409d2dde 100644
--- a/mypy/typeshed/stdlib/socket.pyi
+++ b/mypy/typeshed/stdlib/socket.pyi
@@ -474,6 +474,13 @@ if sys.version_info >= (3, 12):
             ETHERTYPE_VLAN as ETHERTYPE_VLAN,
         )
 
+    if sys.platform == "linux":
+        from _socket import ETH_P_ALL as ETH_P_ALL
+
+    if sys.platform != "linux" and sys.platform != "win32" and sys.platform != "darwin":
+        # FreeBSD >= 14.0
+        from _socket import PF_DIVERT as PF_DIVERT
+
 # Re-exported from errno
 EBADF: int
 EAGAIN: int
@@ -525,6 +532,9 @@ class AddressFamily(IntEnum):
             AF_BLUETOOTH = 32
     if sys.platform == "win32" and sys.version_info >= (3, 12):
         AF_HYPERV = 34
+    if sys.platform != "linux" and sys.platform != "win32" and sys.platform != "darwin" and sys.version_info >= (3, 12):
+        # FreeBSD >= 14.0
+        AF_DIVERT = 44
 
 AF_INET = AddressFamily.AF_INET
 AF_INET6 = AddressFamily.AF_INET6
@@ -577,6 +587,9 @@ if sys.platform != "win32" or sys.version_info >= (3, 9):
 
 if sys.platform == "win32" and sys.version_info >= (3, 12):
     AF_HYPERV = AddressFamily.AF_HYPERV
+if sys.platform != "linux" and sys.platform != "win32" and sys.platform != "darwin" and sys.version_info >= (3, 12):
+    # FreeBSD >= 14.0
+    AF_DIVERT = AddressFamily.AF_DIVERT
 
 class SocketKind(IntEnum):
     SOCK_STREAM = 1
diff --git a/mypy/typeshed/stdlib/sys/__init__.pyi b/mypy/typeshed/stdlib/sys/__init__.pyi
index 353e20c4b2e1..5867c9a9d510 100644
--- a/mypy/typeshed/stdlib/sys/__init__.pyi
+++ b/mypy/typeshed/stdlib/sys/__init__.pyi
@@ -1,9 +1,8 @@
 import sys
 from _typeshed import OptExcInfo, ProfileFunction, TraceFunction, structseq
+from _typeshed.importlib import MetaPathFinderProtocol, PathEntryFinderProtocol
 from builtins import object as _object
 from collections.abc import AsyncGenerator, Callable, Sequence
-from importlib.abc import PathEntryFinder
-from importlib.machinery import ModuleSpec
 from io import TextIOWrapper
 from types import FrameType, ModuleType, TracebackType
 from typing import Any, Final, Literal, NoReturn, Protocol, TextIO, TypeVar, final
@@ -15,10 +14,6 @@ _T = TypeVar("_T")
 _ExitCode: TypeAlias = str | int | None
 _OptExcInfo: TypeAlias = OptExcInfo  # noqa: Y047  # TODO: obsolete, remove fall 2022 or later
 
-# Intentionally omits one deprecated and one optional method of `importlib.abc.MetaPathFinder`
-class _MetaPathFinder(Protocol):
-    def find_spec(self, fullname: str, path: Sequence[str] | None, target: ModuleType | None = ..., /) -> ModuleSpec | None: ...
-
 # ----- sys variables -----
 if sys.platform != "win32":
     abiflags: str
@@ -44,13 +39,13 @@ if sys.version_info >= (3, 12):
     last_exc: BaseException  # or undefined.
 maxsize: int
 maxunicode: int
-meta_path: list[_MetaPathFinder]
+meta_path: list[MetaPathFinderProtocol]
 modules: dict[str, ModuleType]
 if sys.version_info >= (3, 10):
     orig_argv: list[str]
 path: list[str]
-path_hooks: list[Callable[[str], PathEntryFinder]]
-path_importer_cache: dict[str, PathEntryFinder | None]
+path_hooks: list[Callable[[str], PathEntryFinderProtocol]]
+path_importer_cache: dict[str, PathEntryFinderProtocol | None]
 platform: str
 if sys.version_info >= (3, 9):
     platlibdir: str
diff --git a/mypy/typeshed/stdlib/tempfile.pyi b/mypy/typeshed/stdlib/tempfile.pyi
index ce8f2f1f5929..b66369926404 100644
--- a/mypy/typeshed/stdlib/tempfile.pyi
+++ b/mypy/typeshed/stdlib/tempfile.pyi
@@ -374,7 +374,11 @@ class SpooledTemporaryFile(IO[AnyStr], _SpooledTemporaryFileBase):
     def readlines(self, hint: int = ..., /) -> list[AnyStr]: ...  # type: ignore[override]
     def seek(self, offset: int, whence: int = ...) -> int: ...
     def tell(self) -> int: ...
-    def truncate(self, size: int | None = None) -> None: ...  # type: ignore[override]
+    if sys.version_info >= (3, 11):
+        def truncate(self, size: int | None = None) -> int: ...
+    else:
+        def truncate(self, size: int | None = None) -> None: ...  # type: ignore[override]
+
     @overload
     def write(self: SpooledTemporaryFile[str], s: str) -> int: ...
     @overload
diff --git a/mypy/typeshed/stdlib/types.pyi b/mypy/typeshed/stdlib/types.pyi
index f2d79b7f3ade..38940b4345c8 100644
--- a/mypy/typeshed/stdlib/types.pyi
+++ b/mypy/typeshed/stdlib/types.pyi
@@ -1,5 +1,6 @@
 import sys
 from _typeshed import SupportsKeysAndGetItem
+from _typeshed.importlib import LoaderProtocol
 from collections.abc import (
     AsyncGenerator,
     Awaitable,
@@ -16,7 +17,7 @@ from collections.abc import (
 from importlib.machinery import ModuleSpec
 
 # pytype crashes if types.MappingProxyType inherits from collections.abc.Mapping instead of typing.Mapping
-from typing import Any, ClassVar, Literal, Mapping, Protocol, TypeVar, final, overload  # noqa: Y022
+from typing import Any, ClassVar, Literal, Mapping, TypeVar, final, overload  # noqa: Y022
 from typing_extensions import ParamSpec, Self, TypeVarTuple, deprecated
 
 __all__ = [
@@ -64,18 +65,11 @@ _T2 = TypeVar("_T2")
 _KT = TypeVar("_KT")
 _VT_co = TypeVar("_VT_co", covariant=True)
 
-@final
-class _Cell:
-    def __new__(cls, contents: object = ..., /) -> Self: ...
-    def __eq__(self, value: object, /) -> bool: ...
-    __hash__: ClassVar[None]  # type: ignore[assignment]
-    cell_contents: Any
-
 # Make sure this class definition stays roughly in line with `builtins.function`
 @final
 class FunctionType:
     @property
-    def __closure__(self) -> tuple[_Cell, ...] | None: ...
+    def __closure__(self) -> tuple[CellType, ...] | None: ...
     __code__: CodeType
     __defaults__: tuple[Any, ...] | None
     __dict__: dict[str, Any]
@@ -98,7 +92,7 @@ class FunctionType:
         globals: dict[str, Any],
         name: str | None = ...,
         argdefs: tuple[object, ...] | None = ...,
-        closure: tuple[_Cell, ...] | None = ...,
+        closure: tuple[CellType, ...] | None = ...,
     ) -> Self: ...
     def __call__(self, *args: Any, **kwargs: Any) -> Any: ...
     @overload
@@ -318,15 +312,12 @@ class SimpleNamespace:
     def __setattr__(self, name: str, value: Any, /) -> None: ...
     def __delattr__(self, name: str, /) -> None: ...
 
-class _LoaderProtocol(Protocol):
-    def load_module(self, fullname: str, /) -> ModuleType: ...
-
 class ModuleType:
     __name__: str
     __file__: str | None
     @property
     def __dict__(self) -> dict[str, Any]: ...  # type: ignore[override]
-    __loader__: _LoaderProtocol | None
+    __loader__: LoaderProtocol | None
     __package__: str | None
     __path__: MutableSequence[str]
     __spec__: ModuleSpec | None
@@ -336,6 +327,12 @@ class ModuleType:
     # using `builtins.__import__` or `importlib.import_module` less painful
     def __getattr__(self, name: str) -> Any: ...
 
+@final
+class CellType:
+    def __new__(cls, contents: object = ..., /) -> Self: ...
+    __hash__: ClassVar[None]  # type: ignore[assignment]
+    cell_contents: Any
+
 _YieldT_co = TypeVar("_YieldT_co", covariant=True)
 _SendT_contra = TypeVar("_SendT_contra", contravariant=True)
 _ReturnT_co = TypeVar("_ReturnT_co", covariant=True)
@@ -405,7 +402,7 @@ class CoroutineType(Coroutine[_YieldT_co, _SendT_contra, _ReturnT_co]):
 @final
 class MethodType:
     @property
-    def __closure__(self) -> tuple[_Cell, ...] | None: ...  # inherited from the added function
+    def __closure__(self) -> tuple[CellType, ...] | None: ...  # inherited from the added function
     @property
     def __defaults__(self) -> tuple[Any, ...] | None: ...  # inherited from the added function
     @property
@@ -570,8 +567,6 @@ def coroutine(func: Callable[_P, Generator[Any, Any, _R]]) -> Callable[_P, Await
 @overload
 def coroutine(func: _Fn) -> _Fn: ...
 
-CellType = _Cell
-
 if sys.version_info >= (3, 9):
     class GenericAlias:
         @property
diff --git a/mypy/typeshed/stdlib/typing.pyi b/mypy/typeshed/stdlib/typing.pyi
index 4b80397bdd7a..d047f1c87621 100644
--- a/mypy/typeshed/stdlib/typing.pyi
+++ b/mypy/typeshed/stdlib/typing.pyi
@@ -8,7 +8,6 @@ import typing_extensions
 from _collections_abc import dict_items, dict_keys, dict_values
 from _typeshed import IdentityFunction, ReadableBuffer, SupportsKeysAndGetItem
 from abc import ABCMeta, abstractmethod
-from contextlib import AbstractAsyncContextManager, AbstractContextManager
 from re import Match as Match, Pattern as Pattern
 from types import (
     BuiltinFunctionType,
@@ -24,10 +23,10 @@ from types import (
 )
 from typing_extensions import Never as _Never, ParamSpec as _ParamSpec
 
-if sys.version_info >= (3, 10):
-    from types import UnionType
 if sys.version_info >= (3, 9):
     from types import GenericAlias
+if sys.version_info >= (3, 10):
+    from types import UnionType
 
 __all__ = [
     "AbstractSet",
@@ -402,8 +401,8 @@ class Reversible(Iterable[_T_co], Protocol[_T_co]):
     def __reversed__(self) -> Iterator[_T_co]: ...
 
 _YieldT_co = TypeVar("_YieldT_co", covariant=True)
-_SendT_contra = TypeVar("_SendT_contra", contravariant=True)
-_ReturnT_co = TypeVar("_ReturnT_co", covariant=True)
+_SendT_contra = TypeVar("_SendT_contra", contravariant=True, default=None)
+_ReturnT_co = TypeVar("_ReturnT_co", covariant=True, default=None)
 
 class Generator(Iterator[_YieldT_co], Generic[_YieldT_co, _SendT_contra, _ReturnT_co]):
     def __next__(self) -> _YieldT_co: ...
@@ -428,24 +427,28 @@ class Generator(Iterator[_YieldT_co], Generic[_YieldT_co, _SendT_contra, _Return
     @property
     def gi_yieldfrom(self) -> Generator[Any, Any, Any] | None: ...
 
-# NOTE: Technically we would like this to be able to accept a second parameter as well, just
-#   like it's counterpart in contextlib, however `typing._SpecialGenericAlias` enforces the
-#   correct number of arguments at runtime, so we would be hiding runtime errors.
-@runtime_checkable
-class ContextManager(AbstractContextManager[_T_co, bool | None], Protocol[_T_co]): ...
+# NOTE: Prior to Python 3.13 these aliases are lacking the second _ExitT_co parameter
+if sys.version_info >= (3, 13):
+    from contextlib import AbstractAsyncContextManager as AsyncContextManager, AbstractContextManager as ContextManager
+else:
+    from contextlib import AbstractAsyncContextManager, AbstractContextManager
 
-# NOTE: Technically we would like this to be able to accept a second parameter as well, just
-#   like it's counterpart in contextlib, however `typing._SpecialGenericAlias` enforces the
-#   correct number of arguments at runtime, so we would be hiding runtime errors.
-@runtime_checkable
-class AsyncContextManager(AbstractAsyncContextManager[_T_co, bool | None], Protocol[_T_co]): ...
+    @runtime_checkable
+    class ContextManager(AbstractContextManager[_T_co, bool | None], Protocol[_T_co]): ...
+
+    @runtime_checkable
+    class AsyncContextManager(AbstractAsyncContextManager[_T_co, bool | None], Protocol[_T_co]): ...
 
 @runtime_checkable
 class Awaitable(Protocol[_T_co]):
     @abstractmethod
     def __await__(self) -> Generator[Any, Any, _T_co]: ...
 
-class Coroutine(Awaitable[_ReturnT_co], Generic[_YieldT_co, _SendT_contra, _ReturnT_co]):
+# Non-default variations to accommodate couroutines, and `AwaitableGenerator` having a 4th type parameter.
+_SendT_contra_nd = TypeVar("_SendT_contra_nd", contravariant=True)
+_ReturnT_co_nd = TypeVar("_ReturnT_co_nd", covariant=True)
+
+class Coroutine(Awaitable[_ReturnT_co_nd], Generic[_YieldT_co, _SendT_contra_nd, _ReturnT_co_nd]):
     __name__: str
     __qualname__: str
     @property
@@ -457,7 +460,7 @@ class Coroutine(Awaitable[_ReturnT_co], Generic[_YieldT_co, _SendT_contra, _Retu
     @property
     def cr_running(self) -> bool: ...
     @abstractmethod
-    def send(self, value: _SendT_contra, /) -> _YieldT_co: ...
+    def send(self, value: _SendT_contra_nd, /) -> _YieldT_co: ...
     @overload
     @abstractmethod
     def throw(
@@ -473,9 +476,9 @@ class Coroutine(Awaitable[_ReturnT_co], Generic[_YieldT_co, _SendT_contra, _Retu
 # The parameters correspond to Generator, but the 4th is the original type.
 @type_check_only
 class AwaitableGenerator(
-    Awaitable[_ReturnT_co],
-    Generator[_YieldT_co, _SendT_contra, _ReturnT_co],
-    Generic[_YieldT_co, _SendT_contra, _ReturnT_co, _S],
+    Awaitable[_ReturnT_co_nd],
+    Generator[_YieldT_co, _SendT_contra_nd, _ReturnT_co_nd],
+    Generic[_YieldT_co, _SendT_contra_nd, _ReturnT_co_nd, _S],
     metaclass=ABCMeta,
 ): ...