How to test a function with input call?

Question

I have a console program written in Python. It asks the user questions using the command:

some_input = input(\'Answer the question:\', ...)

Answer 1

You can do it with mock.patch as follows.

First, in your code, create a dummy function for the calls to input:

def __get_input(text):
    return input(text)

In your test functions:

import my_module
from mock import patch

@patch('my_module.__get_input', return_value='y')
def test_what_happens_when_answering_yes(self, mock):
    """
    Test what happens when user input is 'y'
    """
    # whatever your test function does

For example if you have a loop checking that the only valid answers are in ['y', 'Y', 'n', 'N'] you can test that nothing happens when entering a different value instead.

In this case we assume a SystemExit is raised when answering 'N':

@patch('my_module.__get_input')
def test_invalid_answer_remains_in_loop(self, mock):
    """
    Test nothing's broken when answer is not ['Y', 'y', 'N', 'n']
    """
    with self.assertRaises(SystemExit):
        mock.side_effect = ['k', 'l', 'yeah', 'N']
        # call to our function asking for input