How to test print statements?

Question

You want to write unittest-cases for a function like that:

def test_me(a):
    for b in c:
        print do_something(a,b)

At firs

Answer 1

In Python 3 it's easy to use unittest.mock on the builtin print function:

from unittest.mock import patch, call

@patch('builtins.print')
def test_print(mocked_print):
    print('foo')
    print()

    assert mocked_print.mock_calls == [call('foo'), call()]

Answer 2

print prints to sys.stdout, which you can reassign to your own object if you wish. The only thing your object needs is a write function which takes a single string argument.

Since Python 2.6 you may also change print to be a function rather than a language construct by adding from __future__ import print_function to the top of your script. This way you can override print with your own function.