Pat,
What you'd want to be testing here is that sum_series works on lucas_nums when you call it with the optional parameters added. 
```
sum_series(input, 2, 1).
```
What you're testing here with your try/except is whether sum_series() does not default to the lucas_nums, which is a good start but you're not testing sum_series' ability to take other parameters which you'll need to do here. Try formatting it like the test on fibo_nums above.