def METHOD_NAME(self):
    """
    Ensures that duplicate bookmarks cannot be created but that the client
    receives the data they would have if it were. We expect it to return 200
    because the request is ultimately OK - but we didn't create anything.
    """
    self.client.post("/api/bookmarks/bookmarks/", self.user1_data, format="json")
    duplicate_response = self.client.post(
        "/api/bookmarks/bookmarks/", self.user1_data, format="json"
    )
    self.assertEqual(duplicate_response.status_code, HTTP_400_BAD_REQUEST)