In chrome/test/data/extensions/api_test/file_system_provider/read_file/test.js between every test the old filesystem is unmounted before mounting the new filesystem. But that can leave the test_util.openedFiles bookkeeping in an inconsistent state as files that are still open at the time of unmounting aren't closed (and when they are closed later the extension isn't informed of this anymore, since the FS is unmounted).