CODEWITHSUNDEEP
pythonassertvalueerror
Robin Andrews
Robin Andrews

Reputation: 3794

Python Assertion for ValueError

Is there a way to use assert in pure Python to test for a ValueError?

E.g. something like:

def try_me():
    raise ValueError("No way Jose")

assert try_me() is ValueError

Upvotes: 2

Views: 3913

Answers (3)

Keith Smith
Keith Smith

Reputation: 21

pytest is a good module to learn for unit testing your code and is very simple for this type of testing. Try this instead:

import pytest
    
with pytest.raises(ValueError):
        try_me()

Upvotes: 0

Andrew Polukhin
Andrew Polukhin

Reputation: 135

You can use unittest.TestCase.assertRaises from the unittest module. Checking if the try_me function raises ValueError looks like this:

import unittest


def try_me():
    raise ValueError("No way Jose")


class MyTestCase(unittest.TestCase):
    def test_if_throws_exception(self):
        self.assertRaises(ValueError, try_me)

Upvotes: 1

Sven Eberth
Sven Eberth

Reputation: 3115

assert evaluates only expressions.

But you can do:

def catch_exception(method):
    try:
        method()
    except Exception as e:
        return e.__class__


def try_me():
    raise ValueError("No way Jose")


assert catch_exception(try_me) is ValueError  # okay
assert catch_exception(try_me) is IndexError  # fails

Upvotes: 0

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