Python多继承单元测试-

Question

我正在尝试理解使用unittest.TestCase类进行多重继承时会发生什么。

MyTest_DoesWork输出了我所期望的，这是setUp()和tearDown()都被触发了。这种情况不会发生在MyTest_DoesNotWork上。为什么会发生这种情况？有什么线索吗？

import unittest

class MyClassTest1(object):
    def setUp(self):
        print 'Setting up', self.__class__
    def test_a1(self):
        print "Running test_a1 for class", self.__class__
    def test_a2(self):
        print "Running test_a2 for class", self.__class__
    def tearDown(self):
        print 'Tearing down', self.__class__

class MyClassTest2(object):
    def setUp(self):
        print 'Setting up', self.__class__
    def test_b1(self):
        print "Running test_b1 for class", self.__class__
    def test_b2(self):
        print "Running test_b2 for class", self.__class__
    def tearDown(self):
        print 'Tearing down', self.__class__

class MyTest_DoesNotWork(unittest.TestCase, MyClassTest1, MyClassTest2):
    """
    Output:
    Running test_a1 for class <class '__main__.MyTest_DoesNotWork'>
    .Running test_a2 for class <class '__main__.MyTest_DoesNotWork'>
    .Running test_b1 for class <class '__main__.MyTest_DoesNotWork'>
    .Running test_b2 for class <class '__main__.MyTest_DoesNotWork'>
    """
    pass

class MyTest_DoesWork(MyClassTest1, MyClassTest2, unittest.TestCase):
    """
    Output:
    Setting up <class '__main__.MyTest_DoesWork'>
    Running test_a1 for class <class '__main__.MyTest_DoesWork'>
    Tearing down <class '__main__.MyTest_DoesWork'>
    .Setting up <class '__main__.MyTest_DoesWork'>
    Running test_a2 for class <class '__main__.MyTest_DoesWork'>
    Tearing down <class '__main__.MyTest_DoesWork'>
    .Setting up <class '__main__.MyTest_DoesWork'>
    Running test_b1 for class <class '__main__.MyTest_DoesWork'>
    Tearing down <class '__main__.MyTest_DoesWork'>
    .Setting up <class '__main__.MyTest_DoesWork'>
    Running test_b2 for class <class '__main__.MyTest_DoesWork'>
    Tearing down <class '__main__.MyTest_DoesWork'>
    """
    pass

if __name__ == "__main__":
    unittest.main()

Answer 1

Python的method resolution order导致了这种情况。对于继承结构，它是按照从左到右声明父类的顺序进行解析的。

因此，对于MyTest_DoesNotWork，python将冲击setUp和tearDown的unittest.TestCase实现，这两个实现什么也不做。因为unittest.TestCase.setUp没有被写成是协作式的，也没有调用其他超类setUp方法，所以它就到此为止了，不会打印任何东西。

对于MyTest_DoesWork，python将首先解析为MyClassTest1。就像unittest.TestCase一样，您还没有编写setUp和tearDown方法来协同调用超类方法。所以它就到此为止了，永远不会调用MyClassTest2方法。所以我猜即使是这样实际上也不会像你预期的那样工作。将您的MyClassTest1 setUp和tearDown方法更改为输出"MyClassTest1“而不是self.class，您将看到它是一直被调用的那个方法。永远不会调用MyClassTest2、setUp和tearDown。