Issue #3259744 by Spokje: PHPUnit 9.5.12 (released 2022-01-21) throws...

      "The \"PHPUnit\Framework\TestSuite\" class is considered internal This class is not covered by the backward compatibility promise for PHPUnit. It may change without further notice. You should not use it from \"Drupal\Tests\TestSuites\TestSuiteBase\".",

      // PHPUnit 9.

      "The \"PHPUnit\TextUI\DefaultResultPrinter\" class is considered internal This class is not covered by the backward compatibility promise for PHPUnit. It may change without further notice. You should not use it from \"Drupal\Tests\Listeners\HtmlOutputPrinter\".",

      "The \"Drupal\Tests\Listeners\DrupalListener\" class implements \"PHPUnit\Framework\TestListener\" that is deprecated.",

      // Guzzle/PSR-7

      "Method \"Psr\Http\Message\StreamInterface::getMetadata()\" will return \"mixed\" as of its next major version. Doing the same in implementation \"GuzzleHttp\Psr7\Stream\" will be required when upgrading.",

    ];