private static void createRegion(GemFireCache cache, String regionName, RegionShortcut shortcut) {
    RegionFactory rf = ((GemFireCacheImpl) cache).createRegionFactory(shortcut);
    System.out.println("created region " + rf.create(regionName));
  }
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