13 files declare their use of BaseFieldOverride

BaseFieldDefinition.php in core/lib/Drupal/Core/Field/BaseFieldDefinition.php
BaseFieldOverrideResourceTestBase.php in core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideResourceTestBase.php
BaseFieldOverrideTest.php in core/modules/jsonapi/tests/src/Functional/BaseFieldOverrideTest.php
BaseFieldOverrideTest.php in core/tests/Drupal/KernelTests/Core/Field/Entity/BaseFieldOverrideTest.php
BaseFieldOverrideValidationTest.php in core/tests/Drupal/KernelTests/Core/Entity/BaseFieldOverrideValidationTest.php
ConfigConfiguratorTest.php in core/tests/Drupal/KernelTests/Core/Recipe/ConfigConfiguratorTest.php
ContentTranslationSettingsTest.php in core/modules/content_translation/tests/src/Functional/ContentTranslationSettingsTest.php
MigrateNodeBundleSettingsTest.php in core/modules/node/tests/src/Kernel/Migrate/d6/MigrateNodeBundleSettingsTest.php
MigrateNodeSettingPromoteTest.php in core/modules/node/tests/src/Kernel/Migrate/d6/MigrateNodeSettingPromoteTest.php
MigrateNodeSettingStatusTest.php in core/modules/node/tests/src/Kernel/Migrate/d6/MigrateNodeSettingStatusTest.php
MigrateNodeSettingStickyTest.php in core/modules/node/tests/src/Kernel/Migrate/d6/MigrateNodeSettingStickyTest.php
MigrateNodeTitleLabelTest.php in core/modules/node/tests/src/Kernel/Migrate/d7/MigrateNodeTitleLabelTest.php
NodeFieldOverridesTest.php in core/modules/node/tests/src/Kernel/NodeFieldOverridesTest.php

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