test(auth): verify no request made when RAB lookup URL is null

Author: macastelaz

packages/google-auth/tests/test__regional_access_boundary_utils.py

@@ -411,6 +411,7 @@ def test_lookup_regional_access_boundary_null_url(self):
         request = mock.Mock()
         result = creds._lookup_regional_access_boundary(request)
         assert result is None
+        request.assert_not_called()
 
     def test_credentials_with_regional_access_boundary_initialization(self):
         creds = CredentialsImpl()