Mock user input()

Question

I am trying to simulate user input for a python script that I have going using py.test. Here's some basic code that represents what I'm trying to accomplish:

def ask():
    while True:
        age = input("Enter your age: ")
        if int(age) < 13:
            print("You are too young")
        else:
            name = input("Enter your name: ")
            break
    print("Welcome!")

I would like to mimic user input and read the output. An example might be something like:

@mock.patch('builtins.input', side_effect=['11'])
def test_invalid_age():
    ask()
    assert stdout == "You are too young"

I've also heard that flexmock might be a better alternative to the built-in unittest mocking system, but I'll take any solution at this point.

Update:

I played around a bit more and have a test that is this:

@mock.patch('builtins.input', side_effect=['11'])
def test_bad_params(self, input):
    ask()
    output = sys.stdout.getline().strip()
    assert output == "You are too young"

When I run py.test I get this result:

E StopIteration /usr/lib/python3.3/unittest/mock.py:904:
StopIteration

It did catch capture the appropriate standard output call as "You are too young".

What exactly is your question? Have you tried to implement this? Did you run the example? What happened? Have a look at e.g. http://stackoverflow.com/q/2617057/3001761 — jonrsharpe, May 04 '15 at 20:39

score 6 · Accepted Answer · answered May 04 '15 at 21:04

ask doesn't return after the first too-young age; it loops until an appropriate age is entered. As written, you'll need to supply all the strings it might read, then do all your assertions after ask returns.

@mock.patch('builtins.input', side_effect=['11', '13', 'Bob'])
def test_bad_params(self, input):
    ask()
    output = sys.stdout.getline().strip()
    assert output == "You are too young"
    # Check the output after "13" and "Bob" are entered as well!
    assert sys.stdout.getline().strip() == "Welcome!"

Mock user input()

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