Contributed by jakzal.
The pcov code coverage extension, as well as the php-dbg debugger, are provided on the image out of the box.
pcov is disabled by default so it doesn't affect performance when it's not needed,
and doesn't break interoperability with other coverage extensions.
It can be enabled by setting pcov.enabled=1:
phpqa php -d pcov.enabled=1 ./vendor/bin/phpunit --coverage-text
Infection users will need to define initial php options:
phpqa /tools/infection run --initial-tests-php-options='-dpcov.enabled=1'