Testing is software development.
Software development is writing code. Testing makes sure the code actually works, so in a nutshell: Testing is software development :-)
Phan is a static analyzer for PHP. Phan project on GitHub It will help you write better PHP7 code. You'll need the Abstract Syntax Tree generated by PHP. You can read a tutorial for how to get Phan working in your project
The MediaWiki project uses Phan. See the article Continuous_integration/Phan