Support running tests in more environments

1. Support running tests in test runners that do not import setuptools
   prior to running the test.

2. Pass along PATH and PYTHONPATH when running setup.py in a new process
   with with a new environment.

setuptools_git_versioning.py

@@ -15,6 +15,11 @@
 from pprint import pformat
 from typing import TYPE_CHECKING, Any, Callable
 
+# because we use distutils in this file, we need to ensure that setuptools is
+# imported first so that it can do monkey patching. this is not always already
+# done for us, for example, when running this in a test or as a module
+import setuptools  # noqa: F401
+
 if TYPE_CHECKING:
     # avoid importing 'packaging' because setuptools-git-versioning can be installed using sdist
     # where 'packaging' is not installed yet

tests/lib/util.py

@@ -30,6 +30,13 @@ def rand_sha() -> str:
 
 def execute(cwd: str | os.PathLike, cmd: str, **kwargs) -> str:
     log.info(f"Executing '{cmd}' at '{cwd}'")
+
+    if "env" in kwargs:
+        kwargs["env"]["PATH"] = os.environ["PATH"]
+        pythonpath = os.getenv("PYTHONPATH", None)
+        if pythonpath:
+            kwargs["env"]["PYTHONPATH"] = pythonpath
+
     return subprocess.check_output(cmd, cwd=cwd, shell=True, universal_newlines=True, **kwargs)  # nosec