Test was run in child process and ended unexpectedly

Did you try just re-running the job? Or does it happen every time?

If it happens every time, maybe we can enable extra debugging on that MR to see what happens: https://docs.gitlab.com/ee/ci/services/#capturing-service-container-logs

It does happen consistently, yes.

Could it be related to the erros in phpstan somehow? https://git.drupalcode.org/project/domain/-/jobs/2511587

I guess it might be related to some error outputting making the job fail but not dumping the information, like suggested here https://stackoverflow.com/questions/69006060/dumping-variables-in-phpuni...

This might even come from core, but in any case, I'd try to address the phpstan errors first to make sure that it's not getting in the way.

@fjgarlin, you were right. The problem was related to the errors reported by phpstan