On the SitePoint PHP blog there's a new tutorial that talks about creating "watchers" in your PHP code similar to the ones that the Javascript world has used to detect changes in files and automatically perform actions.

In the land of JavaScript, it’s not uncommon to preprocess source code. In the land of JavaScript, developers write in syntax not widely supported, and the code is transformed into syntax that is widely supported, usually using a tool called Babel.

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.

The author (Christopher Pitt) then shows how to create the project and make use of pre-processing and some sample scripts to run tests against. He shows how to set up the test configuration and provides an example test. Finally he includes a script that's used by the "watcher" to recompile the scripts before the tests are executed. To to the watching, he uses the yosymfony/resource-watcher package and a long running PHP script ("watch-test").