When running phpunit with code coverage, it runs these checks as documented -- https://xdebug.org/docs/all_functions#xdebug_start_code_coverage

But these variables are not defined with using XDebug 3 with phpunit 8.x, on php7.4

/app # vendor/bin/phpunit -v --coverage-text --coverage-clover  ../build/logs/clover.xml 
PHPUnit 8.5.8 by Sebastian Bergmann and contributors.

Runtime:       PHP 7.4.12 with Xdebug 3.0.0
Configuration: /app/phpunit.xml

Use of undefined constant XDEBUG_CC_UNUSED - assumed 'XDEBUG_CC_UNUSED' (this will throw an Error in a future version of PHP)
/app # grep -r 'XDEBUG_CC_UNUSED' .
./vendor/phpunit/php-code-coverage/src/Driver/Xdebug.php:            \xdebug_start_code_coverage(XDEBUG_CC_UNUSED | XDEBUG_CC_DEAD_CODE);

I found no mention of XDEBUG_CC_DEAD_CODE or XDEBUG_CC_UNUSED being removed in the update logs:

• https://xdebug.org/docs/upgrade_guide
• https://xdebug.org/updates