private static void startCacheServer(GemFireCache cache, int port) throws Exception {
    CacheServer cacheServer = ((GemFireCacheImpl) cache).addCacheServer();
    cacheServer.setPort(port);
    cacheServer.start();
  }
This test starts up multiple servers from the current code base and multiple servers from the
old version and executes puts and gets on a new server and old server and verifies that the
results are present. Note that the puts have overlapping region keys just to test new puts and
replaces
geode-core/src/upgradeTest/java/org/apache/geode/internal/cache/rollingupgrade/RollingUpgrade2DUnitTestBase.java