code: function createStub(client, channel_id, txid, input, proposal) {
      return new Stub(client, channel_id, txid, input, proposal);
  }
docs: /*
  function to create a new Stub, this is done to facilitate unit testing
  
  @param {Handler} client an instance of the Handler class
  @param {string} channel_id channel id
  @param {string} txid transaction id
  @param {any} input decoded message from peer
  @param {any} proposal the proposal
  @returns a new Stub instance