Christoper Pitt published another excellent piece over at Sitepoint. This time he describes how he built a watcher to automatically recompile his preprocessed code and rerun the tests.

In order to reduce the burden of invoking the transformation scripts, boilerplate projects have started to include scripts to automatically watch for file changes; and thereafter invoke these scripts. These projects I’ve worked on have used a similar approach to re-run unit tests. When I change the JavaScript files, these files are transformed and the unit tests are re-run. This way, I can immediately see if I’ve broken anything.

https://www.sitepoint.com/write-javascript-style-test-watchers-php/