4-input.md

Write tests for incorrect input

This assumes you have setup your environment as described in [run_tests.md] and that you are in your virtualenv.

If you get stuck, take a peek at the solution.

1. This time we will be writing tests for safecatmath.py. This module contains a new version of cat_years_to_hooman_years.

2. Look at the existing tests. You can see we have similar test cases to the ones we had for cat_years_to_hooman_years but several more cases have been added:

   • test__cat_years_to_hooman_years__less_0__raises
   • test__cat_years_to_hooman_years__older_than_1000__raises
   • test__cat_years_to_hooman_years__string__raises
   • test__cat_years_to_hooman_years__nan__raises

3. Fill in the body of these tests, using pytest.raises.

4. When you have filled in the body of these tests, run them:

(catpy)user@host:~/catinabox$ python setup.py test

5. When the tests run successfully, push them to your pull request:

(catpy)user@host:~/catinabox$ git commit -a
(catpy)user@host:~/catinabox$ git push origin master

BONUS

Suppose you had to implement the inverse function for cat_years_to_hooman_years, lets call it hooman_years_to_cat_years. Do you think it would be valuable to have a test that does:

assert to_hooman_years(100) == to_cat_years(to_hooman_years(100))

Why or why not? (Hint: what should we trust to absolutely work when we write tests?)

Call us over if you want to chat about this question! Everyone will have different opinions about this.