fs.saveNamespace();
fs.setSafeMode(SafeModeAction.SAFEMODE_LEAVE);
NNStorage storage = spy(cluster.getNameNode().getFSImage().getStorage());
int futureVersion = NameNodeLayoutVersion.CURRENT_LAYOUT_VERSION - 1;
doReturn(futureVersion).when(storage).getServiceLayoutVersion();
storage.writeAll();
cluster.restartNameNode(0, true, "-rollingUpgrade", "downgrade");
} finally {
if (cluster != null) {
cluster.shutdown();
}