Make the mocking more obvious and reliable

Author: danny0838

Lib/test/test_zipfile/test_core.py

@@ -5801,9 +5801,9 @@ def test_append_keep_efs_flag(self):
         efs_flags = [True, True, False, False]
 
         def mock_encode(self):
-            if efs_flags[i]:
-                zinfo.flag_bits |= zipfile._MASK_UTF_FILENAME
-            return (self.filename.encode('ascii'), self.flag_bits)
+            idx = names.index(self.filename)
+            return (self.filename.encode('ascii'), self.flag_bits | (
+                zipfile._MASK_UTF_FILENAME if efs_flags[idx] else 0))
 
         with mock.patch('zipfile.ZipInfo._encodeFilenameFlags', mock_encode), \
              zipfile.ZipFile(TESTFN, "w") as zipfp: