test the failure case

Author: Wulian233

Lib/mimetypes.py

@@ -739,7 +739,6 @@ def _main(args=None):
             else:
                 sys.exit(f"error: media type unknown for {gtype}")
         return '\n'.join(results)
-    return help_text
 
 
 if __name__ == '__main__':

Lib/test/test_mimetypes.py

@@ -478,6 +478,14 @@ def test_multiple_inputs(self):
             "type: image/png encoding: None"
         )
 
+    def test_multiple_inputs_error(self):
+        with self.assertRaises(SystemExit) as err:
+            mimetypes._main(shlex.split("foo.pdf foo.bar_ext"))
+
+        self.assertNotEqual(err.exception.code, 0)
+        self.assertIn("error: media type unknown for foo.bar_ext", str(err.exception))
+
+
     def test_invocation(self):
         for command, expected in [
             ("-l -e image/jpg", ".jpg"),