测试包含在提交db事务后发生的函数调用的django `post_save`信号

Question

在运行django测试时，不提交数据库事务。如何测试对象创建触发的事件，但这发生在提交db事务之后？

我有一个Campaign模型和下面的post_save信号。使用Django TestCase很难断言在创建新的transaction.on_commit对象时调用了transaction.on_commit中的函数。当信号在测试上下文中运行时，它总是认为正在编辑现有的活动对象，而不是新创建的对象。因此，我不能测试if语句的else分支。

如果Campaign.objects.filter(pk=instance.pk).exists()是假的，我如何测试这个案例？

信号：

@receiver(post_save, sender=Campaign, dispatch_uid="apps.writing.signals.create_handwriting")
def create_handwriting(sender, instance, **kwargs):
    """Whenever a campaign is created or updated, trigger the handwriting cloud function to (re)generate the
    handwriting image.
    """

    if Campaign.objects.filter(pk=instance.pk).exists():
        transaction.on_commit(
            lambda: log_campaign_progress(pk=instance.pk, status="t2h-edited", stage="campaign")
        )
        transaction.on_commit(lambda: delete_campaign_pages(campaign_pk=instance.pk))
    else:
        transaction.on_commit(
            lambda: log_campaign_progress(pk=instance.pk, status="t2h-created", stage="campaign")
        )

    transaction.on_commit(lambda: enqueue_handwriting_generation(campaign_pk=instance.pk))

测试：

class TestSignals(TestCase):
    def setUp(self):
        self.factory = RequestFactory()

    @mock.patch("lettergun.apps.writing.signals.log_campaign_progress")
    @mock.patch("lettergun.apps.writing.signals.enqueue_handwriting_generation")
    @mock.patch("lettergun.apps.writing.signals.delete_campaign_pages")
    def test_create_handwriting_edit_existing_campaign(
        self, delete_campaign_pages, enqueue_handwriting_generation, log_campaign_progress
    ):
        # disconnected in the factory so we need to reconnect it here
        signals.post_save.connect(
            sender=Campaign,
            dispatch_uid="apps.writing.signals.create_handwriting",
            receiver=create_handwriting,
        )
        enqueue_handwriting_generation.return_value = True
        log_campaign_progress.return_value = True

        with self.captureOnCommitCallbacks(execute=True) as callbacks:
            user = G(User)
            campaign = G(Campaign, user=user)

        assert Campaign.objects.get(pk=campaign.pk)
        assert Campaign.objects.filter(pk=campaign.pk).exists()

        enqueue_handwriting_generation.assert_called_with(campaign_pk=campaign.pk)
        log_campaign_progress.assert_called_with(pk=campaign.pk, stage="campaign", status="t2h-edited")
        delete_campaign_pages.assert_called_with(campaign_pk=campaign.pk)

Answer 1

django.test.TestCase不支持事务(提交数据库事务并在测试后进行清理会导致性能损失)。根据https://docs.djangoproject.com/en/4.0/topics/testing/tools/#django.test.TestCase

• 将测试封装在两个嵌套的原子()块中:一个用于整个类，另一个用于每个测试。因此，如果要测试某些特定的数据库事务行为，请使用TransactionTestCase.

您应该使用TransactionTestCase https://docs.djangoproject.com/en/4.0/topics/testing/tools/#django.test.TransactionTestCase