Improve GetModuleFileName tests and clarify virtual environment behavior. (#875)

* Add the `GetModuleFileName(None, ...)` test for virtual environments.

* Add a `skipUnless` marker to the `GetModuleFileName` test.

* Rename `GetModuleFileName` tests for clarity.

* Fix `GetModuleFileNameW` API reference URL.

* Clarify `GetModuleFileNameW` behavior in virtual environments.

Author: junkmd

comtypes/test/test_typeinfo.py

@@ -1,4 +1,5 @@
 import ctypes
+import os
 import sys
 import unittest
 from ctypes.wintypes import MAX_PATH
@@ -96,9 +97,19 @@ def test_TypeInfo(self):
 
 
 class Test_GetModuleFileName(unittest.TestCase):
-    def test_null_handler(self):
+    @unittest.skipUnless(
+        sys.prefix == sys.base_prefix,
+        "This will fail in a virtual environment.",
+    )
+    def test_null_handler_sys_executable(self):
         self.assertEqual(GetModuleFileName(None, MAX_PATH), sys.executable)
 
+    def test_null_handler_sys_base_prefix(self):
+        self.assertEqual(
+            os.path.commonpath([GetModuleFileName(None, MAX_PATH), sys.base_prefix]),
+            sys.base_prefix,
+        )
+
     def test_loaded_module_handle(self):
         import _ctypes
 

comtypes/typeinfo.py

@@ -765,9 +765,13 @@ def GetModuleFileName(handle: Optional[int], maxsize: int) -> str:
     """Returns the fullpath of the loaded module specified by the handle.
     If the handle is NULL, returns the executable file path of the current process.
 
-    https://learn.microsoft.com/ja-jp/windows/win32/api/libloaderapi/nf-libloaderapi-loadlibraryw
+    https://learn.microsoft.com/en-us/windows/win32/api/libloaderapi/nf-libloaderapi-getmodulefilenamew
     """
     buf = create_unicode_buffer(maxsize)
+    # In a Python virtual environment on Windows, the Windows API
+    # `GetModuleFileNameW(NULL, ..., ...)` returns the path to the base
+    # `python.exe` (located within `sys.base_prefix`, not same as
+    # `sys.executable`).
     length = _GetModuleFileNameW(handle, buf, maxsize)
     if not length:
         raise ctypes.WinError()