@Override
  public final void preTearDown() throws Exception {
    client1.invoke(OperationsPropagationDUnitTest::closeCache);
    server1.invoke(OperationsPropagationDUnitTest::closeCache);
    server2.invoke(OperationsPropagationDUnitTest::closeCache);
  }
close the caches of the client and the servers
geode-core/src/distributedTest/java/org/apache/geode/internal/cache/ha/OperationsPropagationDUnitTest.java