Regression testing is a software testing process to ensure that code modifications, such as bug fixes or feature updates, haven't negatively impacted or broken previously functioning aspects of the software

How to access private method for testing purpose

 // Create a reflection of the private method to make it accessible for testing.
    $method = new ReflectionMethod(TransformDataForFrontend::class, 'removeUUIDsInString');
    $method->setAccessible(true);

    return $method->invoke((new TransformDataForFrontend), $sql);

PHPunit

./vendor/bin/phpunit --log-events-verbose-text='test.txt' vendor/figma/core/modules/Fe/tests/Unit/FeConfigTest.php

with extending verbose text written to test.txt