16 files declare their use of MigrateProcessInterface in Drupal 8

BlockPluginId.php in core/modules/block/src/Plugin/migrate/process/BlockPluginId.php

BlockVisibility.php in core/modules/block/src/Plugin/migrate/process/BlockVisibility.php

CckFileTest.php in core/modules/file/tests/src/Unit/Plugin/migrate/process/d6/CckFileTest.php

FieldFile.php in core/modules/file/src/Plugin/migrate/process/d6/FieldFile.php

FieldFileTest.php in core/modules/file/tests/src/Unit/Plugin/migrate/process/d6/FieldFileTest.php

FileCopy.php in core/modules/migrate/src/Plugin/migrate/process/FileCopy.php

FileCopyTest.php in core/modules/migrate/tests/src/Unit/process/FileCopyTest.php

FileCopyTest.php in core/modules/migrate/tests/src/Kernel/process/FileCopyTest.php

FilterFormatPermission.php in core/modules/filter/src/Plugin/migrate/process/d6/FilterFormatPermission.php

FilterFormatPermissionTest.php in core/modules/filter/tests/src/Kernel/Migrate/d6/FilterFormatPermissionTest.php

LegacyBlockPluginIdTest.php in core/modules/block/tests/src/Unit/Plugin/migrate/process/LegacyBlockPluginIdTest.php

LegacyBlockVisibilityTest.php in core/modules/block/tests/src/Unit/Plugin/migrate/process/LegacyBlockVisibilityTest.php

MenuLinkParent.php in core/modules/migrate/src/Plugin/migrate/process/MenuLinkParent.php

MenuLinkParentTest.php in core/modules/migrate/tests/src/Unit/process/MenuLinkParentTest.php

MigrateExecutableTest.php in core/modules/migrate/tests/src/Unit/MigrateExecutableTest.php

ProcessPluginBase.php in core/modules/migrate/src/ProcessPluginBase.php