Breaking: #83889 - E_NOTICE free unit testing

Description

Writing unit tests and executing them using the typo3/testing-framework now requires the system under test to no longer raise PHP E_NOTICE level errors, or the test fails.

Impact

This is a first step towards a PHP notice free TYPO3 core.

Affected Installations

Extensions that use the TYPO3 v9 compatible typo3/testing-framework package in a version >= 3.0.0 may see failing unit tests if the tested class raises E_NOTICE errors.

Migration

The best solution is to fix the unit test and/or the system under test to no longer raise E_NOTICE level PHP errors.

In a transition phase, a single unit test case file can set a property to still suppress E_NOTICE warnings:

class FooTest extends \TYPO3\TestingFramework\Core\Unit\UnitTestCase
{
    /**
     * Subject is not notice free, disable E_NOTICES
     */
    protected static $suppressNotices = true;
}

Note that this property is deprecated and will be removed from UnitTestCase as soon as TYPO3 core does not need it anymore.