Hello,

We have enabled parallel runs of PHPUnit extension suite tests for all MediaWiki extensions. This follows after ~3 months of testing on WMDE maintained repositories. We don't anticipate problems, but, if you notice any unusual failures in PHPUnit test suite runs, please file a subtask of T50217: Speed up MediaWiki PHPUnit build by running integration tests in parallel and add @Arthur_Taylor and @kostajh as subscribers. 

https://www.mediawiki.org/wiki/Continuous_integration/Tutorials/Debugging_PHPUnit_Parallel_Test_Failures can also be helpful in debugging.

Cheers,

Arthur, Kosta, and Antoine