The testing framework PHPUnit was added to Drupal 8 in June of 2013. Simpletest is still supported but should only be used for web tests and KernelTests that require a complete or partial Drupal environment.
This handbook section contains documentation specific to Drupal's implementation of PHPUnit. See PHPUnit's documentation for support on writing tests.
Some PHPUnit tests may require specific extensions and if missing those tests will be skipped.
General PHPUnit Resources
- PHPUnit Documentation: http://phpunit.de/manual/4.8/en/index.html
Relevant Drupal issues
- Impending change to file structure: