Check if dict has entry when mock is called

Question

One of my classes needs to do something like this:

class A:
    def __init__(self, someDict, someOtherObject):
        self._someDict = someDict
        self._someOtherObject = someOtherObject

    def func(self):
       self._someDict["key"] = None
       self._someOtherObject.foo()

Now, I would like to check if "key" exists inside the passed dictionary at the moment, foo was called.

class Test( unittest.TestCase ):
    def test_funcShouldAddKeyToDictionaryBeforeCallingFoo(self):
        objectMock = Mock()
        someDict = {}
        aUnderTest = A(someDict, objectMock)

        aUnderTest.func()

        # assert "key" in someDict when called objectMock.foo()

How can I check if the dictionary already has an entry before foo was called?

Answer 1

You can replace foo with your own function that does the check:

class Test(unittest.TestCase):
    def test_funcShouldAddKeyToDictionaryBeforeCallingFoo(self):
        def check_dict():
            self.assertIn("key", someDict)

        objectMock = Mock()
        someDict = {}
        aUnderTest = A(someDict, objectMock)
        objectMock.foo = check_dict  # "check_dict" will be called instead of "foo"
        aUnderTest.func()

This way your check is done at the moment foo would have been called in the tested code, as needed.