Difficulty running tests, --group option not being respected
edit: This might be my issue.


Yes.

The error happens during test discovery, first it has to find all tests and then limit it based on the group.

The easiest workaround is simply to specifiy your module, then you don't even need the group. phpunit will only discover test in that folder, which will not just avoid this problem it will also be much faster.

$ ../vendor/bin/phpunit -c core/phpunit.xml modules/custom/mymodule