In this post on his Medium page Elton Minetto shows how to generate the code coverage of your PHPunit tests with better performance using phpdbg.

In a previous post (in portuguese) I explained how to identify tests that are taking too long to execute. In this post, I’ll show you how to increase the performance of code coverage report generation using PHPUnit.

In the phpunit.xml file it’s possible to add configurations to generate reports related to the tests that are being executed. [...] In addition to changing the phpunit.xml file, to generate this information we also need to install the extension XDebug. However, by installing it we get a substantial decrease in performance.

He shows an example of the time difference in running the tests (about 1 minute without versus 22 with XDebug). He went looking for a better way and found this post talking about using phpdbg instead. He includes the "brew" commands to get everything you'll need installed and how to use phpdbg with your coverage calls rather than XDebug. However, as is pointed out at the end of the post, the results are slightly different but they're close enough to help you know what code to target next.