tests: add a __dir__ check to the __all__test

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

Author: henryiii

Lib/test/test___all__.py

@@ -48,6 +48,7 @@ def check_all(self, modname):
                 raise FailedImport(modname)
         if not hasattr(sys.modules[modname], "__all__"):
             raise NoAll(modname)
+
         names = {}
         with self.subTest(module=modname):
             with warnings_helper.check_warnings(
@@ -72,6 +73,9 @@ def check_all(self, modname):
                 all_set = set(all_list)
                 self.assertCountEqual(all_set, all_list, "in module {}".format(modname))
                 self.assertEqual(keys, all_set, "in module {}".format(modname))
+                # Verify __dir__ is non-empty and doesn't produce an error
+                self.assertTrue(dir(sys.modules[modname]))
+
 
     def walk_modules(self, basedir, modpath):
         for fn in sorted(os.listdir(basedir)):