bpo-46659: Update the test on the mbcs codec alias (GH-31168)

encodings registers the _alias_mbcs() codec search function before
the search_function() codec search function. Previously, the
_alias_mbcs() was never used.

Fix the test_codecs.test_mbcs_alias() test: use the current ANSI code
page, not a fake ANSI code page number.

Remove the test_site.test_aliasing_mbcs() test: the alias is now
implemented in the encodings module, no longer in the site module.

1 files changed, 11 insertions, 6 deletions

diff --git a/Lib/test/test_codecs.py b/Lib/test/test_codecs.py
index 4ad24db..d30ff8f 100644
--- a/Lib/test/test_codecs.py
+++ b/Lib/test/test_codecs.py
@@ -1904,7 +1904,10 @@ class BasicUnicodeTest(unittest.TestCase, MixInCheckStateHandling):
                 name += "_codec"
             elif encoding == "latin_1":
                 name = "latin_1"
-            self.assertEqual(encoding.replace("_", "-"), name.replace("_", "-"))
+            # Skip the mbcs alias on Windows
+            if name != "mbcs":
+                self.assertEqual(encoding.replace("_", "-"),
+                                 name.replace("_", "-"))
 
             (b, size) = codecs.getencoder(encoding)(s)
             self.assertEqual(size, len(s), "encoding=%r" % encoding)
@@ -3188,11 +3191,13 @@ class CodePageTest(unittest.TestCase):
         self.assertEqual(decoded, ('abc', 3))
 
     def test_mbcs_alias(self):
-        # Check that looking up our 'default' codepage will return
-        # mbcs when we don't have a more specific one available
-        with mock.patch('_winapi.GetACP', return_value=123):
-            codec = codecs.lookup('cp123')
-            self.assertEqual(codec.name, 'mbcs')
+        # On Windows, the encoding name must be the ANSI code page
+        encoding = locale.getpreferredencoding(False)
+        self.assertTrue(encoding.startswith('cp'), encoding)
+
+        # The encodings module create a "mbcs" alias to the ANSI code page
+        codec = codecs.lookup(encoding)
+        self.assertEqual(codec.name, "mbcs")
 
     @support.bigmemtest(size=2**31, memuse=7, dry_run=False)
     def test_large_input(self, size):