How can I simulate input to stdin for pyunit?

Question

I\'m trying to test a function that takes input from stdin, which I\'m currently testing with something like this:

cat /usr/share/dict/words | .         


        

Answer 1

Update -- using unittest.mock.patch

Since python 3.3 there is new submodule for unittest called mock that does exactly what you need to do. For those using python 2.6 or above there is a backport of mock found here.

import unittest
from unittest.mock import patch

import module_under_test


class MyTestCase(unittest.TestCase):

    def setUp(self):
        # raw_input is untouched before test
        assert module_under_test.raw_input is __builtins__.raw_input

    def test_using_with(self):
        input_data = "123"
        expected = int(input_data)

        with patch.object(module_under_test, "raw_input", create=True, 
                return_value=expected):
            # create=True is needed as raw_input is not in the globals of 
            # module_under_test, but actually found in __builtins__ .
            actual = module_under_test.function()

        self.assertEqual(expected, actual)

    @patch.object(module_under_test, "raw_input", create=True)
    def test_using_decorator(self, raw_input):
        raw_input.return_value = input_data = "123"
        expected = int(input_data)

        actual = module_under_test.function()

        self.assertEqual(expected, actual)

    def tearDown(self):
        # raw input is restored after test
        assert module_under_test.raw_input is __builtins__.raw_input

if __name__ == "__main__":
    unittest.main()
# where module_under_test.function is:
def function():
    return int(raw_input("prompt> "))

Previous answer -- replacing sys.stdin

I think the sys module might be what you're looking for.

You can do something like

import sys

# save actual stdin in case we need it again later
stdin = sys.stdin

sys.stdin = open('simulatedInput.txt','r') 
# or whatever else you want to provide the input eg. StringIO

raw_input will now read from simulatedInput.txt whenever it is called. If the contents of simulatedInput was

hello
bob

then the first call to raw_input would return "hello", the second "bob" and third would throw an EOFError as there was no more text to read.