模拟一个Python类的方法并返回一个动态值

Question

How can Python's unittest.mock module be used to mock a method that uses a member of the same class?

class NameHelper(object):
    def __init__(self):
        self.local_id = 0

    def next_id(self):
        self.local_id += 1
        return str(self.local_id)

Note, I'm patch.start and patch.stop to do patching in the setUp method:

class TestSomeClient(unittest.TestCase):

    def setUp(self):
        patcher = patch('helpers.name_helper.NameHelper')
        self.addCleanup(patcher.stop)
        self.mock_name_helper = patcher.start()

        # The actual mocked values
        self.mock_name_helper.return_value.local_id = 0
        self.mock_name_helper.return_value.next_id.return_value = 'mock-name'

Clearly, mock-name is not a sensible mock return value. The return value should use the local_id member of NameHelper .

Answer 1

I'm unsure why the question was down-voted with no comments. The answer is, IMO, not clear.

The Python documentation for patch.start and patch.stop , provides the following example for patching in setUp:

class MyTest(TestCase):
     def setUp(self):
         self.patcher1 = patch('package.module.Class1')
         self.MockClass1 = self.patcher1.start()

     def tearDown(self):
         self.patcher1.stop()

MyTest('test_something').run()

However, when patching entire class, this is misleading. The following is more helpful:

class MockClass1():
    pass

class MyTest(TestCase):
    def setUp(self):
        self.patcher1 = patch('package.module.Class1')
        self.MockClass1 = self.patcher1.start()
        self.MockClass1.return_value = MockClass1()

    def tearDown(self):
        self.patcher1.stop()

Note, the additional line:

self.MockClass1.return_value = MockClass1()

The return_value should be a new instance of the class MockClass1 . Applied to my example:

class MockNameHelper(object):
    def __init__(self):
        self.local_id = 0

    def next_id(self):
        self.local_id += 1
        return str(self.local_id)

class TestSomeClient(unittest.TestCase):

    def setUp(self):
        patcher = patch('helpers.name_helper.NameHelper')
        self.addCleanup(patcher.stop)
        self.MockNameHelper = patcher.start()
        self.MockNameHelper.return_value = MockNameHelper()