6 files declare their use of MigrateProcessInterface

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
MigrateExecutableTest.php in core/modules/migrate/tests/src/Unit/MigrateExecutableTest.php
MigrateProcessErrorMessagesTest.php in core/modules/migrate/tests/src/Kernel/MigrateProcessErrorMessagesTest.php
ProcessPluginBase.php in core/modules/migrate/src/ProcessPluginBase.php

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