11 files declare their use of PhpunitCompatibilityTrait in Drupal 8

AppendOpTest.php in core/tests/Drupal/Tests/Composer/Plugin/Scaffold/Integration/AppendOpTest.php

BuildTestBase.php in core/tests/Drupal/BuildTests/Framework/BuildTestBase.php

ComposerHookTest.php in core/tests/Drupal/Tests/Composer/Plugin/Scaffold/Functional/ComposerHookTest.php

DocParserTest.php in core/tests/Drupal/Tests/Component/Annotation/Doctrine/DocParserTest.php

KernelTestBase.php in core/tests/Drupal/KernelTests/KernelTestBase.php

ManageGitIgnoreTest.php in core/tests/Drupal/Tests/Composer/Plugin/Scaffold/Functional/ManageGitIgnoreTest.php

ReplaceOpTest.php in core/tests/Drupal/Tests/Composer/Plugin/Scaffold/Integration/ReplaceOpTest.php

ScaffoldTest.php in core/tests/Drupal/Tests/Composer/Plugin/Scaffold/Functional/ScaffoldTest.php

ScaffoldUpgradeTest.php in core/tests/Drupal/Tests/Composer/Plugin/Scaffold/Functional/ScaffoldUpgradeTest.php

SkipOpTest.php in core/tests/Drupal/Tests/Composer/Plugin/Scaffold/Integration/SkipOpTest.php

SortArrayTest.php in core/tests/Drupal/Tests/Component/Utility/SortArrayTest.php