Python Testing with pytest

Testing for Expected Exceptions

We’ve looked at how any exception can cause a test to fail. But what if a bit of code you are testing is supposed to raise an exception? How do you test for that?

You use pytest.raises() to test for expected exceptions.

As an example, the cards API has a CardsDB class that requires a path argument. What happens if we don’t pass in a path? Let’s try it:

ch2/test_experiment.py

import cards


def test_no_path_fail():
    cards.CardsDB()

$ pytest --tb=short test_experiment.py
===================== test session starts ======================
collected 1 item

test_experiment.py F                                     [100%]

=========================== FAILURES ===========================
______________________ test_no_path_fail _______________________ ...