testing interactive python programs

Question

I would like to know which testing tools for python support the testing of interactive programs. For example, I have an application launched by:

$ python dummy_p         


        

Answer 1

A good example might be the file test_embed.py of the IPython package.

There two different approaches are used:

subprocess

import subprocess
# ...
subprocess.Popen(cmd, env=env, stdin=subprocess.PIPE,
                stdout=subprocess.PIPE, stderr=subprocess.PIPE)
out, err = p.communicate(_exit_cmd_string)

pexpect (as already mentioned by Brian Oakley

import pexpect
# ...
child = pexpect.spawn(sys.executable, ['-m', 'IPython', '--colors=nocolor'],
                          env=env)
# ...
child.sendline("some_command")
child.expect(ipy_prompt)

Answer 2

Your best bet is probably dependency injection, so that what you'd ordinarily pick up from sys.stdin (for example) is actually an object passed in. So you might do something like this:

import sys

def myapp(stdin, stdout):
    print >> stdout, "Hi, what's your name?"
    name = stdin.readline()
    print >> stdout "Hi,", name

# This might be in a separate test module
def test_myapp():
    mock_stdin = [create mock object that has .readline() method]
    mock_stdout = [create mock object that has .write() method]
    myapp(mock_stdin, mock_stdout)

if __name__ == '__main__':
    myapp(sys.stdin, sys.stdout)

Fortunately, Python makes this pretty easy. Here's a more detailed link for an example of mocking stdin: http://konryd.blogspot.com/2010/05/mockity-mock-mock-some-love-for-mock.html

Answer 3

If you are testing an interactive program, consider using expect. It's designed specifically for interacting with console programs (though, more for automating tasks rather than testing).

If you don't like the language expect is based on (tcl) you can try pexpect which also makes it easy to interact with a console program.