6 files declare their use of DefaultTableMapping in Drupal 8

DefaultTableMappingTest.php in core/tests/Drupal/Tests/Core/Entity/Sql/DefaultTableMappingTest.php

EntityViewsDataTest.php in core/modules/views/tests/src/Unit/EntityViewsDataTest.php

Contains \Drupal\Tests\views\Unit\EntityViewsDataTest.

SqlContentEntityStorageSchemaTest.php in core/tests/Drupal/Tests/Core/Entity/Sql/SqlContentEntityStorageSchemaTest.php

SqlContentEntityStorageTest.php in core/tests/Drupal/Tests/Core/Entity/Sql/SqlContentEntityStorageTest.php

Contains \Drupal\Tests\Core\Entity\Sql\SqlContentEntityStorageTest.

ViewsConfigUpdater.php in core/modules/views/src/ViewsConfigUpdater.php

views_test_query_access.module in core/modules/views/tests/modules/views_test_query_access/views_test_query_access.module

Module to test entity query access in Views.