Ref: https://docs.moodle.org/dev/PHPUnit

composer install --dev

php admin/tool/phpunit/cli/init.php

vendor/bin/phpunit theme_squared_coursecattoolbox_testcase theme/squared/tests/coursecattoolbox_test.php
or in Windows:
vendor\bin\phpunit theme_squared_coursecattoolbox_testcase theme/squared/tests/coursecattoolbox_test.php

vendor/bin/phpunit --group theme_squared
or in Windows:
vendor\bin\phpunit --group theme_squared