def METHOD_NAME(self):
    create_user('test')
    form = AuthUserCreateAccountForm({
        'username': 'test',
        'password1': 'unused',
        'password2': 'unused',
        'email': 'unused@example.com'
    })
    self.assertFalse(form.is_valid())
    self.assertIn('username', form.errors)
    self.assertIn('name already exists', form.errors['username'][0])