What is the goal?
The goal of the PHPUnit Initiative is to completely
eradicate deprecate Simpletest in Drupal 8. This would allow Simpletest to be removed from Drupal 9 and move Drupal towards using the industry standard in PHP testing.
What are we doing?
Currently we are working hard to convert all existing Simpletest in core to PHPUnit tests. A lot of work has already been done to make those conversions as painless as possible. But some tests use methods or patterns that are not supported by the new test base or work just slightly different and those need to be modified.
How can I help?
Pick an issue tagged with 'phpunit initiative', and start rolling!
When converting tests, please keep in mind that we want to keep the changes as minimal as possible. Don't update deprecated methods, don't add new docblocks to methods that don't have one, don't rearrange use statements. All that would make these patches bigger then they already are and even harder to review.
Just focus on getting the tests to be green with minimal changes and without loss of coverage.
See the part 'Instructions for converting a Simpletest web test'