void deleteDiskStores() {
    try {
      FileUtils.deleteDirectory(new File(diskDir).getAbsoluteFile());
    } catch (IOException e) {
      throw new Error("Error deleting files", e);
    }
  }
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