code: function describeMessage(message, batch, context) {
    const b = batch || context.batch;
    const state = b && b.states.get(message);
    return message ? `Message (${state && state.msgDesc})` : '';
  }
docs: A `describeItem` implementation that accepts and describes the arguments passed to a "process one message at a time" function.
  @param {Message} message - the message being processed
  @param {Batch} batch - the current batch
  @param {StreamConsumerContext} context - the context to use
  @returns {string} a short description of the message