How do I write a test for an interactive text-based program?

Question

I'm trying to write a test (using unittest) for a simple Python program. It is an interactive program, specifcally it will be a text-based game, for now basically a port of World of Zuul to Python.

So now I want to do good test-driven development and write a test and make sure that when the user inputs command x, that y results happen. Example: when the user inputs "quit", I want the program to end. I want to ensure that behavior. The only problem is, I can't seem to think of a way to give my own program input without actually typing that input into the shell, so I can't think of how to write a test for this.

Currently, I have embedded the program in its own thread... I was thinking this would allow me to asynchronously give it input, but I still don't see how this can be done.

Is there a way to programmatically and dynamically give my own program input? ... Like, using stdin or something? If so I am thoroughly confused, and would appreciate an example.

Finally, if I am on the wrong track here, please tell me, because I am new to both Python and test-driven development, and I would appreciate any suggestions.

Fred Foo · Accepted Answer · 2013-03-14 09:27:12Z

1

You can set up tests that run the program's main function and read the input that the user would provide from a file (or from a string) if you set up the code like this:

def main(inp):
    # play game

if __name__ == '__main__':
    main(sys.stdin)

Then the test involves setting up an input stream (perhaps a StringIO), feeding that to main, and monitoring the output. If you think the program might hang, you can run it in a separate thread and give it a timeout.

If you want to get fancy, you can even use a pty to simulate terminal input.

answered Mar 14, 2013 at 9:27

Fred Foo

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3 Comments

Brian Peterson Over a year ago

I think I see what you're getting at. Feeding from a file would be a super-smart way to do this. But I feel I need to stare down Python docs on I/O for another hour before I actually understand what I need to write inside my test.

Brian Peterson Over a year ago

In essence, I need to have two separate ways to feed my "main" program. One that works under the "if name == 'main'" conditional, for when it is run as a script, and one that I can automate, with a file or a StringIO. Is that what you're saying?

Fred Foo Over a year ago

@Bepetersn: yes, that's what I'm saying. Unit tests are supposed to test small units of the program (usually a class or function), so to use them effectively, you have to set up your program in testable units. Otherwise, you may have to look into other kinds of testing.

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