private void registerForIndirectChange(final Folder folder) {
        //if this PersistableFolder's value is based on another PersistableFolder, then we have to notify on  indirect change
        final PersistableFolder rootPersistableFolder = folder.getRootPersistableFolder();
        if (rootPersistableFolder != null) {
            rootPersistableFolder.registerChangeListener(this, pf -> notifyChanged());
        }
    }
A Folder to use solely for Unit Test
main/src/main/java/cgeo/geocaching/storage/PersistableFolder.java