How can the memoize cache be cleared?

I use the following decorator to cache pure function returns:

def memoize(obj):
    cache = obj.cache = {}

    @functools.wraps(obj)
    def memoizer(*args, **kwargs):
        if args not in cache:
            cache[args] = obj(*args, **kwargs)
        return cache[args]
    return memoizer

It works quite well, but I am running into a problem with unit tests such as this:

class TestFoo(unittest.TestCase):

    def setUp(self):
        # clear the cache here
        pass

    @patch('module1.method1')
    def test_method1_1(self, method1):
        method1.return_value = ""
        d = module1.method2()
        self.assertTrue(len(d) == 0)

    @patch('module1.method1')
    def test_method1_2(self, method1):
        method1.return_value = "TEST1234"
        d = module1.method2()
        self.assertTrue(len(d) == 2)

My problem is that module1.method1 is decorated with memoize, and so from one test to the other, its return value is cached and is not changed with subsequent method1.return_value = "..." assignments.

How can the memoize cache be cleared? When I figure this out I would clear the cache in the setUp method of the test case.