'Try to update a model instance introducing a FK constraint violation.
If it fails it should fail with IntegrityError.'

def test_integrity_checks_on_update(self):

    models.Article.objects.create(headline='Test    article', pub_date=datetime.datetime(2010, 9, 4), reporter=self.r)
    a = models.Article.objects.get(headline='Test    article')
    a.reporter_id = 30
    try:
        a.save()
    except IntegrityError:
        pass
