def METHOD_NAME(self):
    # Set some data
    Cache.set(key='a', value='A', duration=1)
    Cache.set(key='b', value='B', duration=60)
    Cache.set(key='c', value='C', duration=1)
    Cache.set(key='d', value='D', duration=60)
    # Check it's all stored
    self.assertIn('a', Cache._cache_.keys())
    self.assertIn('b', Cache._cache_.keys())
    self.assertIn('c', Cache._cache_.keys())
    self.assertIn('d', Cache._cache_.keys())
    # Wait for expiry then clean the cache
    time.sleep(2)
    Cache.clean()
    # Only unexpired data still present
    self.assertNotIn('a', Cache._cache_.keys())
    self.assertIn('b', Cache._cache_.keys())
    self.assertNotIn('c', Cache._cache_.keys())
    self.assertIn('d', Cache._cache_.keys())