Install and configure a remote file system where a newly created file will be local readable only. E.g. https://github.com/catalyst/moodle-tool_objectfs   Set $CFG->alternative_file_system_class to this new file system. Since  MDL-58068 this will be used during unit tests. Assert that core_files_file_storage_testcase::test_update_reference_internal and core_filelib_testcase::test_file_merge_files_from_draft_area_into_filearea throw errors because the files are not remotely readable. implement fix. Run tests again and assert these errors are not thrown.