def test_raises_error_without_field(self):
    msg = 'At least one field is required to define an index.'
    with self.assertRaisesMessage(ValueError, msg):
        models.Index()
def test_raises_error_without_field(self):
    msg = 'At least one field is required to define an index.'
    with self.assertRaisesMessage(ValueError, msg):
        models.Index()