static void makeSureHelixBalance(VcrServer vcrServer, StrictMatchExternalViewVerifier helixBalanceVerifier) {
    Assert.assertTrue("Helix topology change timeout.",
        TestUtils.checkAndSleep(true, () -> vcrServer.getVcrClusterParticipant().getAssignedPartitionIds().size() > 0,
            15000));
    assertTrue("Helix balance timeout.", helixBalanceVerifier.verify(15000));
  }
Helper function to make sure helix rebalanced.
@param vcrServer a sample server to detect ideal state change.
@param helixBalanceVerifier helix balance verifier.
ambry-vcr/src/test/java/com/github/ambry/vcr/VcrBackupTest.java