How to supply stdin, files and environment variable inputs to Python unit tests?

Question

How to write tests where conditions like the following arise:

1. Test user Input.
2. Test input read from a file.
3. Test input read from an environme

Answer 1

If you are tied to using raw_input (or any other specific input source), I'm a big proponent of the mock library. Given the code that Mark Rushakoff used in his example:

def say_hello():
    name = raw_input("What is your name? ")
    return "Hello " + name

Your test code could use mock:

import mock

def test_say_hello():
     with mock.patch('__builtin__.raw_input', return_value='dbw'):
         assert say_hello() == 'Hello dbw'

     with mock.patch('__builtin__.raw_input', side_effect=['dbw', 'uki']):
         assert say_hello() == 'Hello dbw'
         assert say_hello() == 'Hello uki'

These assertions would pass. Note that side_effect returns the elements of the list in order. It can do so much more! I'd recommend checking out the documentation.