Django单元测试类

2019-01-17

TestCase与TransactionTestCase都是继承自SimpleTestCase,两者主要的区别在于:

  • TestCase在测试开始时,判断当前连接的数据库是否支持事务特性,如支持,则开启事务操作;在测试结束时,同样判断是否支持事务特性,如支持,执行事务回滚,然后关闭所有链接。具体setUpClass与tearDownClass方法如下
@classmethod
    def setUpClass(cls):
        super(TestCase, cls).setUpClass()
        if not connections_support_transactions():  # 事务支持判断
            return
        cls.cls_atomics = cls._enter_atomics()  # 开启事务,TestCase中测试代码均处于此事务Block中

        if cls.fixtures:
            for db_name in cls._databases_names(include_mirrors=False):
                    try:
                        call_command('loaddata', *cls.fixtures, **{
                            'verbosity': 0,
                            'commit': False,
                            'database': db_name,
                        })
                    except Exception:
                        cls._rollback_atomics(cls.cls_atomics)
                        raise
        cls.setUpTestData()


@classmethod
def tearDownClass(cls):
    if connections_support_transactions():  # 事务支持判断
        cls._rollback_atomics(cls.cls_atomics)  # 回滚所有操作
        for conn in connections.all():  # 关闭所有链接
            conn.close()
    super(TestCase, cls).tearDownClass()
  • TransactionTestCase与TestCase不同,在此测试类中并不开启事务块,测试结束时通过进行Fush操作清空数据。此类没有重写SimpleTestCase的setUp和tearDown方法,只修改了_post_teardown等如下:
def _post_teardown(self):
    """
    * 清空数据库的内容
    * 关闭链接
    """
    try:
        self._fixture_teardown()
        super(TransactionTestCase, self)._post_teardown()
        if self._should_reload_connections():
            for conn in connections.all():
                conn.close()
    finally:
        if self.available_apps is not None:
            apps.unset_available_apps()
            setting_changed.send(sender=settings._wrapped.__class__,
                                 setting='INSTALLED_APPS',
                                 value=settings.INSTALLED_APPS,
                                 enter=False)


def _fixture_teardown(self):
    for db_name in self._databases_names(include_mirrors=False):
        call_command('flush', verbosity=0, interactive=False,
                     database=db_name, reset_sequences=False,
                     allow_cascade=self.available_apps is not None,
                     inhibit_post_migrate=self.available_apps is not None)

在事务方面的区别使得:使用TestCase时,如果被测试代码中出现必须在事务块中执行的代码,则会抛出异常,如官方举例的select_for_update():

class SampleTestCase(TestCase):
    def setUp(self):
        Sample.objects.create(**{'field1': 'value1, 'field2': 'value2'})

    def test_difference_testcase(self):
        sample = Sample.objects.select_for_update().filter()
        print(sample)


class SampleTransactionTestCase(TransactionTestCase):
    def setUp(self):
        Sample.objects.create(**{'field1': 'value1, 'field2': 'value2'})

    def test_difference_transactiontestcase(self):
        sample = Sample.objects.select_for_update().filter()
        print(sample)

第一个TestCase会抛出异常:

AssertionError: TransactionManagementError not raised

第二个TTC会通过测试。

小结

  • 使用TestCase,相当于后续代码都会处于一个外层事务的Block内执行,因此测试者不能测试必须运行在事务Block中的代码 (For instance, you cannot test that a block of code is executing within a transaction, as is required when using select_for_update())
  • TestCase中,最终事务需要进行回滚,因此如果在测试代码中进行了conn.close()一类的操作将会引起异常
  • TransactionTestCase不开启事务,并且通过测试结束时Flush DB的方案来还原干净环境