a little madness

Recently I’ve been cooking up some new acceptance-level tests for Pulse. The sort of tests that need to take a Pulse release package, unpack it, start the server and poke it with a stick. This is the sort of automation that I would typically use bash for: since a lot of the work involves executing and managing subprocess. However, I had learned from earlier testing that process control from bash is not very portable. More specifically, the behaviour of Cygwin bash on Windows differs considerably from *nix bash. At the time, I worked around the problem by doing some process control using Ant, but there had to be a better way.

Enter Python. Or, more specifically, the new(ish) subprocess module (introduced in Python 2.4). With this module Python finally has a concise but powerful way to launch and control subprocesses. It also includes convenient ways to handle subprocess I/O, including setting up pipelines. What’s more, I have so far found it to be quite portable between Linux and Windows.

Starting with something simple, let’s say you just want to launch a command synchronously (much as you would in a shell script):

Simple. Want to set up a pipeline like `dmesg | grep hda` (capturing the final output)? Here’s an example straight from the doco:

For my specific case, I used the ability to launch a Pulse server processes in the background and capture the output extensively. When done, I shut down the server using the standard shutdown script (testing of said script being a nice side-effect). An asynchronous child is started simply by creating a Popen object:

I have simplified this example a bit, but the real work is all there, and it’s pleasantly straightforward. This combined well with Python’s simple XML-RPC API, which I used to manipulate the running server.

So far the switch to from bash/Ant to Python has been a great success. If you need a cross-platform way to automate your acceptance testing, give it a go.

This entry was posted on Thursday, September 28th, 2006 at 11:42 pm and is filed under Agile, Project Automation, Python, Technology, Testing. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.