'All the items from left list that don\'t match
any item from the right list.'

def test_get_changed_items(self):

    listA = [1, 2, 3, 4, 5, 8, 9]
    listB = [1, 2, 3, 4, 5, 6, 7]
    want = [8, 9]
    got = _get_changed_items(listA, listB)
    self.assertEqual(want, got)
    tags_to_add = ['one', 'two']
    existing_tags = ['two']
    want = ['one']
    got = _get_changed_items(tags_to_add, existing_tags)
    self.assertEqual(want, got)
    tags_to_remove = ['one', 'two']
    existing_tags = ['two', 'three']
    want = ['three']
    got = _get_changed_items(existing_tags, tags_to_remove)
    self.assertEqual(want, got)
