When we use gem parallel_tests our application in test environment used, for example, 8 parallel processes. But webpacker compiling the same files at the same time in each process. This is bad and can lead to unexpected errors.

Also when assets did not change, we do not want to spend time compiling them.

Hi, today I want speak about slow specs. It's very an unpleasant situation when specs run very slowly and spend many time for build (15-20 or more minutes). One way to remedy this situation it's a split specs into groups and running on multiple CPU cores. For this we can use gem parallel_tests.