gh-131290: ensure that test files can be executed as standalone scripts (#131371)

---------

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

Lib/test/test_metaclass.py

@@ -297,4 +297,6 @@ def load_tests(loader, tests, pattern):
 
 
 if __name__ == "__main__":
+    # set __name__ to match doctest expectations
+    __name__ = "test.test_metaclass"
     unittest.main()

Lib/test/test_pyclbr.py

@@ -3,7 +3,9 @@
    Nick Mathewson
 '''
 
+import importlib.machinery
 import sys
+from contextlib import contextmanager
 from textwrap import dedent
 from types import FunctionType, MethodType, BuiltinFunctionType
 import pyclbr
@@ -22,6 +24,29 @@
 # is imperfect (as designed), testModule is called with a set of
 # members to ignore.
 
+
+@contextmanager
+def temporary_main_spec():
+    """
+    A context manager that temporarily sets the `__spec__` attribute
+    of the `__main__` module if it's missing.
+    """
+    main_mod = sys.modules.get("__main__")
+    if main_mod is None:
+        yield  # Do nothing if __main__ is not present
+        return
+
+    original_spec = getattr(main_mod, "__spec__", None)
+    if original_spec is None:
+        main_mod.__spec__ = importlib.machinery.ModuleSpec(
+            name="__main__", loader=None, origin="built-in"
+        )
+    try:
+        yield
+    finally:
+        main_mod.__spec__ = original_spec
+
+
 class PyclbrTest(TestCase):
 
     def assertListEq(self, l1, l2, ignore):
@@ -145,6 +170,7 @@ def test_easy(self):
         self.checkModule('pyclbr')
         # XXX: Metaclasses are not supported
         # self.checkModule('ast')
+        with temporary_main_spec():
             self.checkModule('doctest', ignore=("TestResults", "_SpoofOut",
                                                 "DocTestCase", '_DocTestSuite'))
         self.checkModule('difflib', ignore=("Match",))
@@ -223,6 +249,7 @@ def test_others(self):
         with warnings.catch_warnings():
             warnings.simplefilter('ignore', DeprecationWarning)
             cm('sre_parse', ignore=('dump', 'groups', 'pos')) # from sre_constants import *; property
+        with temporary_main_spec():
             cm(
                 'pdb',
                 # pyclbr does not handle elegantly `typing` or properties

Lib/test/test_regrtest.py

@@ -2546,4 +2546,5 @@ def test_test_result_get_state(self):
 
 
 if __name__ == '__main__':
+    setup.setup_process()
     unittest.main()

Misc/NEWS.d/next/Tests/2025-03-17-19-47-27.gh-issue-131290.NyCIXR.rst

@@ -0,0 +1 @@
+Tests in :file:`Lib/test` can now be correctly executed as standalone scripts.