Restore patching

I like mocking and patching in unittest. And you shouldn’t forget to restore all the patchings also. I would think it should be put in the TearDown() method in a unittest. But it seems that I was wrong.

From the official document:

…This method will only be called if the setUp() succeeds, regardless of the outcome of the test method…

So if there is an exception in setUp(), the patchings will not be restored. The correct way of doing it should be using the addCleanup() method.

…If setUp() fails, meaning that tearDown() is not called, then any cleanup functions added will still be called.

And example if you use patch() as function.

class MyTest(TestCase):
  def setUp(self):
    patcher = patch('package.module.Class')
    self.MockClass = patcher.start()

Mock the base class

I am not sure if you should do that since I haven’t found too many articles on the internet. But I will put it here anyway. The base classes are defined in a class’s __bases__ attribute, but when I tried to patch it like other attribute using:

@mock.patch.object(ExtendedClass, '__bases__', (MockBaseClass,))

I got a TypeError:

TypeError: can't delete ExtendedClass.__bases__

Looks like mock module is trying to remove it before reassign it. I had struggled for a few hours before I found out another simple way to do it:

ExtendedClass.__bases__ = (MockBaseClass,)

The only drawback is that you will have to restore the base class manually afterwards.