I released GreenRocket library on October 2012. It is a dead simple implementation of Observer design pattern, which I use in almost all of my projects. I thought, there was nothing to improve. But my recent project heavily uses the library. And I get tired to write tests that checks signals. This is how them look like:

from nose import tools
# I use Nose for testing my code

from myproject import MySignal, some_func
# ``MySignal`` inherits ``greenrocket.Signal``
# ``some_func`` must fire ``MySignal`` as its side-effect


def test_some_func():
    log = []                    # Create log for fired signals

    @MySignal.subscribe         # Subscribe a dummy handler
    def handler(signal):
        log.append(signal)      # Put fired signal to the log

    some_func()                 # Call the function to test

    # Test fited signal from the log
    tools.eq_(len(log), 1)
    tools.eq_(log[0].x, 1)
    tools.eq_(log[0].y, 2)
    # ...and so on

There are four lines of utility code. And it is boring. So I added helper class Watchman to the library to make it testing friendly. This is how it works:

from greenrocket import Watchman

from myproject import MySignal, some_func


def test_some_code_that_fires_signal():
    watchman = Watchman(MySignal)           # Create a watchman for MySignal
    some_func()
    watchman.assert_fired_with(x=1, y=2)    # Test fired signal

Just one line of utility code and one line for actual test! I have already rewritten all of my tests. So if you are using the library, it’s time to upgrade. If you don’t, then try it out.