At the last ChiPy meeting there was a presentation by Fawad Halim on the python-mock mock object library.

While I usually abhor complex mock libraries, that one actually looked quite good and sufficiently simple. But I also thought it could be a lot simpler using doctest.

So after the meeting I whipped up minimock. Here's what a test looks like; first some setup:

>>> smtplib.SMTP = Mock('smtplib.SMTP')
>>> smtplib.SMTP.mock_returns = Mock('smtp_connection')

Then the test:

>>> send_email('ianb@colorstudy.com', 'joe@example.com',
...            'Hi there!', 'How is it going?')
Called smtplib.SMTP('localhost')
Called smtp_connection.sendmail(
    'ianb@colorstudy.com',
    ['joe@example.com'],
    'To: joe@example.com\nFrom: ianb@colorstudy.com\nSubject: Hi there!\n\nHow is it going?')
Called smtp_connection.quit()

It's about 25 lines of actual code and I believe supports all the patterns that python-mock supports. Almost all features are actually implicit features of doctest. You really want to set the ELLIPSIS option (which I prefer to use in all my doctests).

Why people don't implement doctest in other language, I have no idea. It's totally translatable and it's so damn simple. You don't have to understand all sorts of ideas; the ideas just fall out of doctest (like this mocking). Maybe it's too simple for anyone to feel proud of porting it. It's not a whole new concept in testing (*coughyagnicough*). It's just a simple idea that, once you figure it out, feels like it should have been obvious all along.