private static void closeCache(GemFireCache cache) {
    if (cache == null) {
      return;
    }
    boolean cacheClosed = cache.isClosed();
    if (!cacheClosed) {
      stopCacheServers(cache);
      cache.close();
    }
    cache = null;
  }
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