Properties getClientSystemProperties() {
    Properties p = new Properties();
    p.setProperty("mcast-port", "0");
    p.setProperty(DistributionConfig.LOG_LEVEL_NAME, DUnitLauncher.logLevel);
    return p;
  }
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