PCOV support was merged into PHPUnit 8, and I strongly encourage you to upgrade to PHPUnit 8 ... however ...
Since for some people, this is turning out to be a nightmare because of the usage of void, and type system rules; Here is a package that will clobber the Xdebug driver in version 5, 6 and 7 of PHPUnit.
composer require pcov/clobber in your project, this will install the drivers in your vendor directory and in addition, it will install bin/pcov.
To clobber the Xdebug driver in the current directory:
vendor/bin/pcov clobber
To unclobber the Xdebug driver (revert changes):
vendor/bin/pcov unclobber
To clobber the Xdebug driver in another directory:
vendor/bin/pcov /path/to/source clobber
To unclobber the Xdebug driver in another directory:
vendor/bin/pcov /path/to/source unclobber
Note: pcov/clobber needs to be a dependency in any directory where bin/pcov operates.