'Failing unique for date validation should result in field error.'

def test_is_not_unique_for_date(self):

    data = {'slug': 'existing', 'published': '2000-01-01'}
    serializer = UniqueForDateSerializer(data=data)
    assert (not serializer.is_valid())
    assert (serializer.errors == {'slug': ['This    field    must    be    unique    for    the    "published"    date.']})
