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

composer install --dev

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

Linux:
vendor/bin/phpunit format_flexible_courseformatlib_testcase course/format/flexible/tests/courseformatlib_test.php
or
Windows:
vendor\bin\phpunit format_flexible_courseformatlib_testcase course/format/flexible/tests/courseformatlib_test.php

Linux:
vendor/bin/phpunit --group format_flexible
or
Windows:
vendor\bin\phpunit --group format_flexible
