coffee-grinder coffee-grinder - 6 months ago 27
Python Question

Using unittest.mock to patch input() in Python 3

How do you use the @patch decorator to patch the built-in input() function?

For example, here's a function in question.py that I'd like to test, which contains a call to input():

def query_yes_no(question, default="yes"):
""" Adapted from http://stackoverflow.com/questions/3041986/python-command-line-yes-no-input """

valid = {"yes": True, "y": True, "ye": True, "no": False, "n": False}
if default is None:
prompt = " [y/n] "
elif default == "yes":
prompt = " [Y/n] "
elif default == "no":
prompt = " [y/N] "
else:
raise ValueError("invalid default answer: '%s'" % default)

while True:
sys.stdout.write(question + prompt)
choice = input().lower()

if default is not None and choice == '':
return valid[default]
elif choice in valid:
return valid[choice]
else:
sys.stdout.write("Please respond with 'yes' or 'no' "
"(or 'y' or 'n').\n")


Here's my test, which gives me the error "ImportError: No module named 'builtins'":

import unittest
from unittest.mock import patch

import question

class TestQueryYesNo(unittest.TestCase):

@patch('__builtins__.input.return_value', 'y')
def test_query_y(self):
answer = question.query_yes_no("Blah?")
self.assertTrue(answer)

Answer

__builtin__ module is renamed to builtins in Python 3. Replace as follow:

@patch('builtins.input', lambda: 'y')