gh-93096: fix test_mimetypes.test_guess_type_conflicting_with_mimetypes

Lib/mimetypes.py

@@ -669,7 +669,7 @@ def _default_mime_types():
 _default_mime_types()
 
 
-def _main():
+def _main(args=None):
     """Run the mimetypes command-line interface."""
     import sys
     from argparse import ArgumentParser
@@ -686,22 +686,24 @@ def _main():
         help='additionally search for common but non-standard types'
     )
     parser.add_argument('type', nargs='+', help='a type to search')
-    args = parser.parse_args()
+    args = parser.parse_args(args)
 
     if args.extension:
         for gtype in args.type:
             guess = guess_extension(gtype, not args.lenient)
             if guess:
                 print(guess)
             else:
-                sys.exit(f"error: unknown type {gtype}")
+                # do not use parser.error() as it prints a help message
+                parser.exit(1, f"error: unknown type {gtype}\n")
     else:
         for gtype in args.type:
             guess, encoding = guess_type(gtype, not args.lenient)
             if guess:
                 print('type:', guess, 'encoding:', encoding)
             else:
-                sys.exit(f"error: media type unknown for {gtype}")
+                # do not use parser.error() as it prints a help message
+                parser.exit(1, f"error: media type unknown for {gtype}\n")
 
 
 if __name__ == '__main__':

Lib/test/test_mimetypes.py

@@ -1,14 +1,13 @@
+import contextlib
 import io
 import mimetypes
 import os
 import sys
 import unittest.mock
-from os import linesep
-
+from platform import win32_edition
 from test import support
 from test.support import os_helper
 from test.support.script_helper import run_python_until_end
-from platform import win32_edition
 
 try:
     import _winapi
@@ -392,9 +391,19 @@ def test__all__(self):
 
 class MimetypesCliTestCase(unittest.TestCase):
 
-    def mimetypes_cmd(cls, *args, **kwargs):
-        result, _ = run_python_until_end('-m', 'mimetypes', *args)
-        return result.rc, result.out.decode(), result.err.decode()
+    def mimetypes_cmd(self, *args):
+        # We cannot use run_python_until_end() as the latter would not
+        # call setUpModule() which unsets mimetypes.knowfiles. Instead,
+        # we need to directly call the main() function in order to avoid
+        # re-initializing the database.
+        rc, out, err = 0, io.StringIO(), io.StringIO()
+        with contextlib.redirect_stdout(out), contextlib.redirect_stderr(err):
+            try:
+                mimetypes._main(args)
+            except SystemExit as exc:
+                self.assertIsInstance(exc.code, int)
+                rc = exc.code
+        return rc, out.getvalue(), err.getvalue()
 
     def test_help_option(self):
         retcode, out, err = self.mimetypes_cmd('-h')
@@ -411,34 +420,31 @@ def test_invalid_option(self):
     def test_guess_extension(self):
         retcode, out, err = self.mimetypes_cmd('-l', '-e', 'image/jpg')
         self.assertEqual(retcode, 0)
-        self.assertEqual(out, f'.jpg{linesep}')
+        self.assertEqual(out, '.jpg\n')
         self.assertEqual(err, '')
 
         retcode, out, err = self.mimetypes_cmd('-e', 'image/jpg')
         self.assertEqual(retcode, 1)
         self.assertEqual(out, '')
-        self.assertEqual(err, f'error: unknown type image/jpg{linesep}')
+        self.assertEqual(err, 'error: unknown type image/jpg\n')
 
         retcode, out, err = self.mimetypes_cmd('-e', 'image/jpeg')
         self.assertEqual(retcode, 0)
-        self.assertEqual(out, f'.jpg{linesep}')
+        self.assertEqual(out, '.jpg\n')
         self.assertEqual(err, '')
 
     def test_guess_type(self):
         retcode, out, err = self.mimetypes_cmd('-l', 'foo.webp')
         self.assertEqual(retcode, 0)
-        self.assertEqual(out, f'type: image/webp encoding: None{linesep}')
+        self.assertEqual(out, 'type: image/webp encoding: None\n')
         self.assertEqual(err, '')
 
-    @unittest.skipIf(
-        sys.platform == 'darwin',
-        'macOS lists common_types in mime.types thus making them always known'
-    )
     def test_guess_type_conflicting_with_mimetypes(self):
         retcode, out, err = self.mimetypes_cmd('foo.pic')
         self.assertEqual(retcode, 1)
         self.assertEqual(out, '')
-        self.assertEqual(err, f'error: media type unknown for foo.pic{linesep}')
+        self.assertEqual(err, 'error: media type unknown for foo.pic\n')
+
 
 if __name__ == "__main__":
     unittest.main()