gh-127636: Clarify the trailing-slash tarfile test

Note that './mydir/' is a regular-file member, not DIRTYPE, so a future
reader does not turn it into a directory and lose the regression
coverage.  Also assert the member actually extracts as a file rather
than only checking that extract() does not raise.

Author: gpshead

Lib/test/test_tarfile.py

@@ -255,12 +255,17 @@ def test_add_dir_getmember(self):
         self.add_dir_and_getmember('a'*101)
 
     def test_extract_name_with_trailing_slash(self):
+        # gh-127636: './mydir/' is deliberately a regular-file member
+        # (REGTYPE, not DIRTYPE) whose stored name ends in a slash.  It
+        # extracts as a file.  Do not "fix" this by setting DIRTYPE; the
+        # trailing-slash name on a non-directory is what is being tested.
         with tarfile.open(tmpname, 'w') as tar:
             tar.addfile(tarfile.TarInfo('./mydir/'))
-        with tarfile.open(tmpname) as tar:
+        with os_helper.temp_dir() as tmpdir, tarfile.open(tmpname) as tar:
             names = tar.getnames()
             self.assertEqual(names, ['./mydir/'])
-            tar.extract(names[0], TEMPDIR, filter='fully_trusted')
+            tar.extract(names[0], tmpdir, filter='fully_trusted')
+            self.assertTrue(os.path.isfile(os.path.join(tmpdir, 'mydir')))
 
     @unittest.skipUnless(hasattr(os, "getuid") and hasattr(os, "getgid"),
                          "Missing getuid or getgid implementation")