This used to improve testing speed, however, after upgrading to Laravel 5.6 the speed improvement is gone. Not sure what I'm missing but in my case the test time jumped to 3 minutes (5.6) from 40 seconds (5.5).
@hughsaffar - did you switch to Argon? Or still using Bcrypt?
@laurencei I tried both and got the same result.
@hughsaffar I think it's best to report an issue so @taylorotwell can have a look at it 🙂