Try to be a little more resilient to errors. This might help the test

pass, but my guess is that it won't.  I'm guessing that some other
test is leaving this file open which means it can't be removed
under Windows AFAIK.

Lib/test/test_mailbox.py

@@ -694,7 +694,7 @@ class _TestMboxMMDF(TestMailbox):
         self._box.close()
         self._delete_recursively(self._path)
         for lock_remnant in glob.glob(self._path + '.*'):
-            os.remove(lock_remnant)
+            test_support.unlink(lock_remnant)
 
     def test_add_from_string(self):
         # Add a string starting with 'From ' to the mailbox
@@ -915,7 +915,7 @@ class TestBabyl(TestMailbox):
         self._box.close()
         self._delete_recursively(self._path)
         for lock_remnant in glob.glob(self._path + '.*'):
-            os.remove(lock_remnant)
+            test_support.unlink(lock_remnant)
 
     def test_labels(self):
         # Get labels from the mailbox