[MNT] sync differential testing utilities with sktime (#434)

This PR syncs differential testing utilities with `sktime` anticipating
a joint refactor to `skbase`.

Counterpart of sktime/sktime#6840

Modules affected:

* `skpro.tests.test_switch`
* `skpro.utils.git_diff`

skpro/tests/test_switch.py

@@ -1,6 +1,8 @@
 # copyright: skpro developers, BSD-3-Clause License (see LICENSE file)
-# based on utility from sktime of the same name
-"""Switch utility for determining whether tests for a class should be run or not."""
+"""Switch utility for determining whether tests for a class should be run or not.
+
+Module does not contain tests, only test utilities.
+"""
 
 __author__ = ["fkiraly"]
 
@@ -27,17 +29,17 @@ def run_test_for_class(cls, return_reason=False):
     2. Condition 2:
 
       If the module containing the class/func has changed according to is_class_changed,
-      or one of the modules containing any parent classes in sktime,
+      or one of the modules containing any parent classes in the local package,
       then condition 2 is met.
 
     3. Condition 3:
 
-      If the object is an sktime ``BaseObject``, and one of the test classes
+      If the object is an skpro ``BaseObject``, and one of the test classes
       covering the class have changed, then condition 3 is met.
 
     4. Condition 4:
 
-      If the object is an sktime ``BaseObject``, and the package requirements
+      If the object is an skpro ``BaseObject``, and the package requirements
       for any of its dependencies have changed in ``pyproject.toml``,
       condition 4 is met.
 
@@ -51,7 +53,7 @@ def run_test_for_class(cls, return_reason=False):
       If ``ONLY_CHANGED_MODULES`` is False, this condition is always True.
 
     Also checks whether the class or function is on the exclude override list,
-    EXCLUDE_ESTIMATORS in sktime.tests._config (a list of strings, of names).
+    EXCLUDE_ESTIMATORS in skpro.tests._config (a list of strings, of names).
     If so, the tests are always skipped, irrespective of the other conditions.
 
     Parameters
@@ -160,7 +162,6 @@ class for which to determine whether it should be tested
 
         If multiple reasons are present, the first one in the above list is returned.
     """
-
     from skpro.tests.test_all_estimators import ONLY_CHANGED_MODULES
     from skpro.utils.git_diff import get_packages_with_changed_specs, is_class_changed
     from skpro.utils.validation._dependencies import _check_estimator_deps
@@ -174,18 +175,18 @@ def _required_deps_present(obj):
         else:
             return True
 
-    def _is_class_changed_or_parents(cls):
-        """Check if class or any of its sktime parents have changed, return bool."""
+    def _is_class_changed_or_local_parents(cls):
+        """Check if class or any of its local parents have changed, return bool."""
         # if cls is a function, not a class, default to is_class_changed
         if not isclass(cls):
             return is_class_changed(cls)
 
         # now we know cls is a class, so has an mro
         cls_and_parents = getmro(cls)
-        cls_and_parents = [
+        cls_and_local_parents = [
             x for x in cls_and_parents if x.__module__.startswith(LOCAL_PACKAGE)
         ]
-        return any(is_class_changed(x) for x in cls_and_parents)
+        return any(is_class_changed(x) for x in cls_and_local_parents)
 
     def _tests_covering_class_changed(cls):
         """Check if any of the tests covering cls have changed, return bool."""
@@ -231,19 +232,58 @@ def _is_impacted_by_pyproject_change(cls):
         return True, "True_pyproject_change"
 
     # Condition 3:
-    # if the object is an sktime BaseObject, and one of the test classes
+    # if the object is an skpro BaseObject, and one of the test classes
     # covering the class have changed, then run the test
     cond3 = _tests_covering_class_changed(cls)
     if cond3:
         return True, "True_changed_tests"
 
     # Condition 2:
     # any of the modules containing any of the classes in the list have changed
-    # or any of the modules containing any parent classes in sktime have changed
-    cond2 = _is_class_changed_or_parents(cls)
+    # or any of the modules containing any parent classes in local package have changed
+    cond2 = _is_class_changed_or_local_parents(cls)
     if cond2:
         return True, "True_changed_class"
 
     # if none of the conditions are met, do not run the test
     # reason is that there was no change
     return False, "False_no_change"
+
+
+def run_test_module_changed(module):
+    """Check if test should run based on module changes
+
+    This switch can be used to decorate tests not pertaining to a specific class.
+
+    The function can be used to switch tests on and off
+    based on whether a target module has changed.
+
+    This checks whether the module ``module``, or any of its child modules,
+    have changed.
+
+    If ``ONLY_CHANGED_MODULES`` is False, the test is always run,
+    i.e., this function always returns True.
+
+    Parameters
+    ----------
+    module : string, or list of strings
+        modules to check for changes, e.g., ``skpro.regression``
+
+    Returns
+    -------
+    bool : switch to run or skip the test
+        True iff: at least one of the modules or its submodules have changed,
+        or if ``ONLY_CHANGED_MODULES`` is False
+    """
+    from skpro.tests.test_all_estimators import ONLY_CHANGED_MODULES
+    from skpro.utils.git_diff import is_module_changed
+
+    # if ONLY_CHANGED_MODULES is off: always True
+    # tests are always run if soft dependencies are present
+    if not ONLY_CHANGED_MODULES:
+        return True
+
+    if not isinstance(module, (list, tuple)):
+        module = [module]
+
+    return any(is_module_changed(mod) for mod in module)

skpro/utils/git_diff.py

@@ -45,7 +45,10 @@ def get_path_from_module(module_str):
             raise ImportError(
                 f"Error in get_path_from_module, module '{module_str}' not found."
             )
-        return module_spec.origin
+        module_path = module_spec.origin
+        if module_path.endswith("__init__.py"):
+            return module_path[:-11]
+        return module_path
     except Exception as e:
         raise ImportError(f"Error finding module '{module_str}'") from e
 
@@ -54,6 +57,8 @@ def get_path_from_module(module_str):
 def is_module_changed(module_str):
     """Check if a module has changed compared to the main branch.
 
+    If a child module has changed, the parent module is considered changed as well.
+
     Parameters
     ----------
     module_str : str