@Override
  public final void preTearDown() {
    try {
      if (!FailOverDetectionByCCU) {
        ClientServerObserverHolder.setInstance(oldBo);
      }

      FailOverDetectionByCCU = false;

      // close the clients first
      closeCache();

      // then close the servers
      server0.invoke(RedundancyLevelTestBase::closeCache);
      server1.invoke(RedundancyLevelTestBase::closeCache);
      server2.invoke(RedundancyLevelTestBase::closeCache);
      server3.invoke(RedundancyLevelTestBase::closeCache);
    } finally {
      CacheServerTestUtil.enableShufflingOfEndpoints();
    }

    CacheServerTestUtil.resetDisableShufflingOfEndpointsFlag();
  }
@param connectedServers is the expected number of connected servers (1 or more)
@param redundantServers is the expected number of redundant servers (0 or more)
geode-core/src/distributedTest/java/org/apache/geode/internal/cache/tier/sockets/RedundancyLevelTestBase.java