Having a lot of migrations might slow down your tests. My colleague Alex shares how you can fix this.
One of the larger test suites I run daily has about 1500 tests in it. It takes just over 4 minutes to complete at an average of 160ms per test. That's pretty good. However, lately I've noticed a delay between starting PHPUnit and running the first test. This delay grew to the point where running a single test would take almost 12 seconds with the setUp method using most of that time on... migrations.