Those of you that have been around the PHP community for any significant period of time have likely come across Xdebug, which is more or less the gold standard for debugging and development tooling for the language. This post is not the place to scratch the surface of that issue, but suffice it to say that recording every function call, execution path, and variable assignment and profiling your code is no small feat. The issue that I stumbled upon over the weekend was in a large factor of the Laravel Scheduled Task montioring SaaS Jake and I have been working on, thenping.me.
But there's just needless layers of interruption on top of your workflow when all you want to do is get an understanding of your test coverage.
If you're after something that is going to give you just the coverage data - and something you can put into a CI process to track that your coverage doesn't go down over time, without blowing out your test suite, perhaps consider pcov over Xdebug.