Testing Python Exceptions

Python’s py.test provides a helper to test code raises the right exceptions.

import pytest

def test_divide():
    with pytest.raises(ZeroDivisionError) as excinfo:
        1 / 0

The pytest.raises helper will fail a test if the error is not raised.

The excinfo value contains info about the error for more asserts. It has the following properties:

value

An instance of the error caught by py.test.

type

The class of the error instance.

traceback

The traceback of the error instance.

import pytest

def test_divide():
    with pytest.raises(ZeroDivisionError) as excinfo:
        1 / 0
    assert 'division by zero' in str(excinfo.value)