private String parseSingleMessage(String msgStr) {
    JsonParser parser = new JsonParser();
    JsonArray msgArray = (JsonArray) parser.parse(msgStr);
    JsonObject msg = (JsonObject) msgArray.get(0);

    return msg.get("message").getAsString();
  }
Tests that when there is no revertable upgrade, a reversion of a specific
ugprade ID is not allowed.
ambari-server/src/test/java/org/apache/ambari/server/controller/internal/UpgradeResourceProviderTest.java