7 files declare their use of CacheContextInterface

BookNavigationCacheContext.php in core/modules/book/src/Cache/BookNavigationCacheContext.php
CacheContextsManagerTest.php in core/tests/Drupal/Tests/Core/Cache/Context/CacheContextsManagerTest.php
Contains \Drupal\Tests\Core\Cache\Context\CacheContextsManagerTest.
ConfigOverrideIntegrationTestCacheContext.php in core/modules/config/tests/config_override_integration_test/src/Cache/ConfigOverrideIntegrationTestCacheContext.php
EntityTestViewGrantsCacheContext.php in core/modules/system/tests/modules/entity_test/src/Cache/EntityTestViewGrantsCacheContext.php
PirateDayCacheContext.php in core/modules/config/tests/config_override_test/src/Cache/PirateDayCacheContext.php
ViewsTestCacheContext.php in core/modules/views/tests/modules/views_test_data/src/Cache/ViewsTestCacheContext.php
WorkspaceCacheContext.php in core/modules/workspaces/src/WorkspaceCacheContext.php

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