Unit testing is one of the most important features you have to write when developing a library. GLib have a test suite and is available for GLib based libraries for a while, and it is available for Vala libraries too.
Now I’ve finished a patch to add Unit Testing to Vala libraries templates in GNOME Builder. Hope it is clean and easy to use, even for other projects not using Builder as primary IDE.
This template should be available on Builder 3.22 and will help you, Vala developer, to setup your Vala libraries easy and start to write down your tests cases for bug hunting, regression-free releases and better experience for your users.