Tools of the Trade: vl_cruise_control

This is the first in what should become a series on various tools we’ve developed here at Viget and are sharing with the community through our open source repository. While we’ve been diligently creating code, we haven’t always been as good at telling people about it—so here’s an effort to correct that oversight. Late last year, we installed and enthusiastically adopted the CruiseControl.rb package for continuous integration. Out of the box, CC.rb runs your test suite and reports when tests fail. This has encouraged us to write better tests and run them more often before we commit code. We’ve also used rcov to check our test coverage, finding those parts of the code where our testing was inadequate, but we weren’t using rcov consistently. Two great tools that could work better together—how could we make our code even better by combining the two? The answer is vl_cruise_control, a Rails plugin that uses rcov to enforce a coverage target, and causes CC.rb to mark a build as failed if that target isn’t met. So in addition to regularly checking that all the tests pass, we also check that all (or substantially all) of our code is accounted for in our tests. vl_cruise_control is intentionally easy to install and use. Just install rcov on your CC.rb system:

sudo gem install rcov 

Then check out the plugin into your Rails application’s vendor/plugins directory, and add a line to your Rakefile defining your coverage target:

require_coverage '95%' 

Once that line is added, the plugin will define a Rake task called cruise, which will automatically be picked up by CC.rb and run in place of the default test suite every time it detects a new revision. If any of the tests fail, or if the coverage calculated by rcov falls below your threshold, Rake will exit with an error and CC.rb will fail the build. Otherwise, the build passes. It’s really just that simple. It works great with standard Test::Unit tests as well as RSpec. We’ve been using this plugin to great success. We started a few projects with a target of 95%. Once we met 95%, we stepped it up to 98%. And now we’re aiming for the full 100%. Granted, test coverage is just one metric and doesn’t, by itself, guarantee anything about the quality of the code or its tests. But it encourages good habits in developers, and when vl_cruise_control makes checking coverage so easy, it’s hard to argue against it.