@asadoughi 

Thank you for letting me know about mock's side_effect feature. ```side_effect``` only works if the method in question is called more than once inside the current running test.  The only way to use that feature as such:

```python
sub_find.side_effect = [subnet, []]
```

is if we combine the test functions together (and call delete_subnet before create_subnet).

Since setUp is called before each test function, that means only the first item in the side_effect list would be used for that particular test. Am I missing something?