如何断言已引发 HTTP 异常？

Question

I'm making an HTTP request using the requests library. If the request fails, an exception is raised. For example (truncated and simplified):

main.py

from requests import get


def make_request():
    r = get("https://httpbin.org/get")
    r.raise_for_status()

I've written a test using pytest that mocks the request.

test_main.py

from unittest import mock
from unittest.mock import patch

import pytest
from requests import HTTPError

from main import make_request


@patch("main.get")
def test_main_exception(mock_get):
    exception = HTTPError(mock.Mock(status=404), "not found")
    mock_get(mock.ANY).raise_for_status.side_effect = exception

    make_request()

However, I'm getting the following error because the exception is raised in the test—causing the test to fail.

$ pytest
...
E               requests.exceptions.HTTPError: [Errno <Mock id='4352275232'>] not found

/usr/local/Cellar/python/3.7.2_1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/unittest/mock.py:1011: HTTPError
==================================================== 1 failed in 0.52s ====================================================

How do I assert on the behavior that occurs when an HTTP exception is raised (eg 404 status code)?

Answer 1

Use the pytest.raises context manager to capture the exception and assert on the error message. For example:

with pytest.raises(HTTPError) as error_info:
    make_request()
    assert error_info == exception

Full example:

test_main.py

from unittest import mock
from unittest.mock import patch

import pytest
from requests import HTTPError

from main import make_request


@patch("main.get")
def test_main_exception(mock_get):
    exception = HTTPError(mock.Mock(status=404), "not found")
    mock_get(mock.ANY).raise_for_status.side_effect = exception

    with pytest.raises(HTTPError) as error_info:
        make_request()
        assert error_info == exception

See pytest - Assertions about expected exceptions for more info.