PHPUnit: refactor internals for large-scale automation

[epdenouden]

PHPUnit, the unit testing framework for PHP
Project website: https://phpunit.de/
Repository: https://github.com/sebastianbergmann/phpunit/

Challenge description
Development of PHP applications has changed a lot as frameworks and infrastructure matures. Applications and test collections have grown and continuous integration is mostly done on rented on-demand infrastructure.

As a result developer behaviour has shifted towards more of a "let the pipeline and auto-scalers sort it out", often resulting in very slow test collections that are only usable because of third party hosted pipelines like GitHub/Gitlab/Travis.

Related issues

• Working draft for Event subsystem: Make TestHook interfaces as easy to use as TestListener sebastianbergmann/phpunit#3390 with a first pull Working draft for Event subsystem theseer/phpunit#1
• Extend dependency checker: Using @depends to depend on classes sebastianbergmann/phpunit#3519
• Refactor data providers: Reduce resource footprint of data-driven tests sebastianbergmann/phpunit#3736

[jfhovinne]

Closing, see #19