'If a field raises a validation error, but does not have a corresponding
error message, then raise an appropriate assertion error.'

def test_invalid_error_key(self):

    with pytest.raises(AssertionError) as exc_info:
        self.field.to_native(123)
    expected = 'ValidationError    raised    by    `ExampleField`,    but    error    key    `incorrect`    does    not    exist    in    the    `error_messages`    dictionary.'
    assert (str(exc_info.value) == expected)
