def METHOD_NAME(self):
    fid = open(self.FIXTURE_FILENAME, 'rb')
    data = MultiDict([
        ('file', fid),
        ('language', ModelLanguage.CellML.name),
    ])
    endpoint = '/model/validate'
    with app.app.app.test_client() as client:
        response = client.post(endpoint, data=data, content_type="multipart/form-data")
    fid.close()
    self.assertEqual(response.status_code, 200, response.json)
    validation_report = response.json
    self.assertEqual(validation_report['status'], "invalid")
    self.assertIn('The default namespace must be', json.dumps(validation_report['errors']))