16 files declare their use of ContentEntityBase

Comment.php in core/modules/comment/src/Entity/Comment.php
ContentEntityBaseUnitTest.php in core/tests/Drupal/Tests/Core/Entity/ContentEntityBaseUnitTest.php
ContentModerationState.php in core/modules/content_moderation/src/Entity/ContentModerationState.php
EntityTest.php in core/modules/system/tests/modules/entity_test/src/Entity/EntityTest.php
EntityTestUpdate.php in core/modules/system/tests/modules/entity_test_update/src/Entity/EntityTestUpdate.php
EntityTestWithBundle.php in core/modules/system/tests/modules/entity_test/src/Entity/EntityTestWithBundle.php
Feed.php in core/modules/aggregator/src/Entity/Feed.php
File.php in core/modules/file/src/Entity/File.php
Item.php in core/modules/aggregator/src/Entity/Item.php
Message.php in core/modules/contact/src/Entity/Message.php
NoLanguageEntityTest.php in core/modules/language/tests/language_test/src/Entity/NoLanguageEntityTest.php
PathAlias.php in core/modules/path_alias/src/Entity/PathAlias.php
Shortcut.php in core/modules/shortcut/src/Entity/Shortcut.php
StringIdEntityTest.php in core/modules/migrate/tests/modules/migrate_entity_test/src/Entity/StringIdEntityTest.php
User.php in core/modules/user/src/Entity/User.php
Workspace.php in core/modules/workspaces/src/Entity/Workspace.php

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