def METHOD_NAME(self):
    form = PageUpdateForm(
        data={
            "url": "/this_url_is_more_than_100_characters_long_which_is_invalid"
            "_because_the_model_field_has_a_max_length_of_100",
            "title": "Title",
            "content": "Content",
        }
    )
    self.assertFalse(form.is_valid())
    self.assertEqual(
        form.errors["url"],
        ["Ensure this value has at most 100 characters (it has 107)."],
    )