Warning in tests "THE ERROR HANDLER HAS CHANGED!"

Describe the bug When running a functional test I get an error printed THE ERROR HANDLER HAS CHANGED!

The error comes from the phpunit-bridge, the code around the message is:

screen shot 2018-05-14 at 4 43 46 pm

Still looking into why this happens as i'm porting our tests from the core patch to these traits, if anyone has any clues let me know.