Verify the error code or message from SystemExit in pytest

James Mills' answer doesn't answer the question fully. capsys is the easy bit.

As mentioned in the comment by mvr, to get the exit code returned, do this:

with pytest.raises(SystemExit) as excinfo:
    run_something()

assert excinfo.value.code == 1

This works with the latest pytest:

All you need to do is run pytest with the --capture=sys option and dependent the assertion outside of the raises() context (this bit is important for some reason!)

Example:

#!/usr/bin/env python

from __future__ import print_function

import pytest


def f(code=0):
    print("Foo")
    raise SystemExit(code)


def test_f(capsys):
    with pytest.raises(SystemExit):
        f()
    out, err = capsys.readouterr()
    assert out == "Foo\n"
    print(out, err)

Demo:

$ py.test -v --capture=sys test_foo.py 
======================================= test session starts ========================================
platform linux2 -- Python 2.7.9 -- py-1.4.27 -- pytest-2.7.0 -- /home/prologic/.virtualenvs/test/bin/python
rootdir: /home/prologic/tmp, inifile: 
collected 1 items 

test_foo.py::test_f PASSED

===================================== 1 passed in 0.00 seconds =====================================

Changing the print("Foo") to print("Bar") results in:

$ py.test -v --capture=sys test_foo.py 
======================================= test session starts ========================================
platform linux2 -- Python 2.7.9 -- py-1.4.27 -- pytest-2.7.0 -- /home/prologic/.virtualenvs/test/bin/python
rootdir: /home/prologic/tmp, inifile: 
collected 1 items 

test_foo.py::test_f FAILED

============================================= FAILURES =============================================
______________________________________________ test_f ______________________________________________

capsys = <_pytest.capture.CaptureFixture instance at 0x7f2729405518>

    def test_f(capsys):
        with pytest.raises(SystemExit):
            f()
        out, err = capsys.readouterr()
>       assert out == "Foo\n"
E       assert 'Bar\n' == 'Foo\n'
E         - Bar
E         + Foo

test_foo.py:17: AssertionError
===================================== 1 failed in 0.01 seconds =====================================

Which I think is exactly what you were after!

I did this in a clean virtualenv:

mkvirtualenv test
pip install pytest

The trick here is to read and understand Setting capturing methods or disabling capturing