CODEWITHSUNDEEP
pythonpytest
snazzybouche
snazzybouche

Reputation: 2426

Assert exception message?

I'm using pytest in a project with a good many custom exceptions.

pytest provides a handy syntax for checking that an exception has been raised, however, I'm not aware of one that asserts that the correct exception message has been raised.

Say I had a CustomException that prints "boo!", how could I assert that "boo!" has indeed been printed and not, say, "<unprintable CustomException object>"?

#errors.py
class CustomException(Exception):
    def __str__(self): return "ouch!"

#test.py
import pytest, myModule

def test_custom_error(): # SHOULD FAIL
    with pytest.raises(myModule.CustomException):
        raise myModule.CustomException == "boo!"

Upvotes: 16

Views: 15476

Answers (2)

manu datta
manu datta

Reputation: 151

You can use match keyword in raises. Try something like

with pytest.raises(
        RuntimeError, match=<error string here>
    ):
     pass

Upvotes: 9

Tom Dalton
Tom Dalton

Reputation: 6190

I think what you're looking for is:

def failer():
    raise myModule.CustomException()

def test_failer():
    with pytest.raises(myModule.CustomException) as excinfo:
        failer()

    assert str(excinfo.value) == "boo!"

Upvotes: 24

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