Python: Write unittest for console print

Question

Function foo prints to console. I want to test the console print. How can I achieve this in python?

Need to test this function, has NO return statement

Answer 1

If you happen to use pytest, it has builtin output capturing. Example (pytest-style tests):

def eggs():
    print('eggs')


def test_spam(capsys):
    eggs()
    captured = capsys.readouterr()
    assert captured.out == 'eggs\n'

You can also use it with unittest test classes, although you need to passthrough the fixture object into the test class, for example via an autouse fixture:

import unittest
import pytest


class TestSpam(unittest.TestCase):

    @pytest.fixture(autouse=True)
    def _pass_fixtures(self, capsys):
        self.capsys = capsys

    def test_eggs(self):
        eggs()
        captured = self.capsys.readouterr()
        self.assertEqual('eggs\n', captured.out)

Check out Accessing captured output from a test function for more info.