public static List<VmConfiguration> upgrades() {
    return ALL_CONFIGURATIONS.stream()
        .filter(isUpgrade())
        .collect(toList());
  }
Returns the list of VM configurations suitable for use as starting configurations in upgrade
tests. Each upgrade configuration has either an old version of Geode or an old version of
Java, but not both.

@return the list of VM configurations suitable for upgrade tests
geode-junit/src/main/java/org/apache/geode/test/version/VmConfigurations.java