I'm having trouble figuring how I would test a library that intended to be used for communicating with another web service. For example, I have a Messenger class that initializes a connection and requires a configuration and a remote address to run. How would I go about testing something like this?

import { MessengerConfig } from '../Interfaces/MessengerConfig';
import { Connection, ConfirmChannel, connect } from 'amqplib';
import * as Promise from 'bluebird';

export default class Messenger {

    connection: Connection;
    channel: ConfirmChannel;
    config: MessengerConfig;

    constructor(logger, config: MessengerConfig) {
        this.logger = logger;
        this.connection = null;
        this.channel = null;
        this.config = config;

    public start(durable: boolean = true): Promise<any> {
        return connect(this.config.host)
            .then((conn) => {
                this.connection = conn;
                return this.connection.createConfirmChannel();
            .then((chan) => {
                this.channel = chan;
                return this.channel.prefetch(1);
            .then(() => {
                return Promise.map(this.config.subKeys, (route) => {
                    return this.channel.assertExchange(route.exchange, 'direct', { durable: durable });


What could I change to test the start function? Or is that even worth testing? In .NET this was a bit easier because I could create overloaded constructors to inject a mock HttpClient or whatever I needed. I can't overload functions in typescript/javascript like I would there, though.


Yeah seems a little pointless to mock all the library objects. You'd end up with a test which just tested your mock.

I would mock the rabbitmq server with a local one that returned dummy data and do an integration test

  • 1
    That's probably as good an approach as any, though to be fair, if you trust a library so little that you feel a suite of tests is required solely to test the library itself, then perhaps it's time to choose a different library. – Robert Harvey Jul 26 '17 at 23:36
  • well there is some stuff in there to test. like the route setup – Ewan Jul 27 '17 at 6:17
  • This seems to be the way I want to go. Need to figure out a way to mock a rabbitmq server in node though. Thanks! – Cuthbert Jul 28 '17 at 14:52
  • use a real one in a test env and inject a random queue name – Ewan Jul 28 '17 at 17:29

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