How to test a promise that connects to RabbitMQ?

Question

Hi I'm using Chai and trying to test a custom function that connects to RabbitMQ passing a wrong host:

connect(host) {
    return new Promise((resolve, reject) => {
      amqp.connect(host)
        .then((conn) => {
          resolve(conn);
        })
        .catch((err) => {
          throw new Error(err);
        });
    });
  }

If the connection fail I throw a Error, so I'm testing it like this:

it('shouldnt connect to RabbitMQ service successfully with the wrong host.', async () => {
      const result = await rabbitmqmailer.connect('amqp://wronghost');
      expect(result).to.equal(Error);
    });

The connection fails and throws a error but my test is not testing that, simply I got the exception on my terminal:

RabbitMQMailer component.
    RabbitMQMailer configuration information.
      ✓ should test rabbitmqmailer host configuration.
      ✓ should test rabbitmqmailer queue configuration.
      ✓ should get rabbitmqmailer empty emailContent value after make a new instance.
      ✓ should get rabbitmqmailer empty emailContentConsumed value after make a new instance.
      ✓ resolves
      ✓ should connect to RabbitMQ service successfully with the correct host. (60ms)
Unhandled rejection Error: Error: getaddrinfo EAI_AGAIN wronghost wronghost:5672
    at _amqplib2.default.connect.then.catch.err (/home/ubuntu/Desktop/easy-tracking/backend/src/components/rabbitmqmailer/rabbitmqmailer.dal.js:1:11069)
    at tryCatcher (/home/ubuntu/Desktop/easy-tracking/backend/node_modules/amqplib/node_modules/bluebird/js/release/util.js:16:23)
    at Promise._settlePromiseFromHandler (/home/ubuntu/Desktop/easy-tracking/backend/node_modules/amqplib/node_modules/bluebird/js/release/promise.js:512:31)
    at Promise._settlePromise (/home/ubuntu/Desktop/easy-tracking/backend/node_modules/amqplib/node_modules/bluebird/js/release/promise.js:569:18)
    at Promise._settlePromise0 (/home/ubuntu/Desktop/easy-tracking/backend/node_modules/amqplib/node_modules/bluebird/js/release/promise.js:614:10)
    at Promise._settlePromises (/home/ubuntu/Desktop/easy-tracking/backend/node_modules/amqplib/node_modules/bluebird/js/release/promise.js:690:18)
    at _drainQueueStep (/home/ubuntu/Desktop/easy-tracking/backend/node_modules/amqplib/node_modules/bluebird/js/release/async.js:138:12)
    at _drainQueue (/home/ubuntu/Desktop/easy-tracking/backend/node_modules/amqplib/node_modules/bluebird/js/release/async.js:131:9)
    at Async._drainQueues (/home/ubuntu/Desktop/easy-tracking/backend/node_modules/amqplib/node_modules/bluebird/js/release/async.js:147:5)
    at Immediate.Async.drainQueues [as _onImmediate] (/home/ubuntu/Desktop/easy-tracking/backend/node_modules/amqplib/node_modules/bluebird/js/release/async.js:17:14)
    at processImmediate (timers.js:632:19)

      1) shouldnt connect to RabbitMQ service successfully with the wrong host.

I tried catching the exception on a trycatch block but it's the same issue.

EDIT: I got this error on terminal after changing my test to:

it('shouldnt connect to RabbitMQ service successfully with the wrong host.', async (done) => {
      const result = await rabbitmqmailer.connect('amqp://wronghost');
      expect(result).to.be.an.instanceof(Error);
      done();
    });


(node:18911) UnhandledPromiseRejectionWarning: Error: Error: getaddrinfo EAI_AGAIN wronghost wronghost:5672
    at _amqplib2.default.connect.then.catch.err (/home/ubuntu/Desktop/easy-tracking/backend/src/components/rabbitmqmailer/rabbitmqmailer.dal.js:1:11475)
    at tryCatcher (/home/ubuntu/Desktop/easy-tracking/backend/node_modules/amqplib/node_modules/bluebird/js/release/util.js:16:23)
    at Promise._settlePromiseFromHandler (/home/ubuntu/Desktop/easy-tracking/backend/node_modules/amqplib/node_modules/bluebird/js/release/promise.js:512:31)
    at Promise._settlePromise (/home/ubuntu/Desktop/easy-tracking/backend/node_modules/amqplib/node_modules/bluebird/js/release/promise.js:569:18)
    at Promise._settlePromise0 (/home/ubuntu/Desktop/easy-tracking/backend/node_modules/amqplib/node_modules/bluebird/js/release/promise.js:614:10)
    at Promise._settlePromises (/home/ubuntu/Desktop/easy-tracking/backend/node_modules/amqplib/node_modules/bluebird/js/release/promise.js:690:18)
    at _drainQueueStep (/home/ubuntu/Desktop/easy-tracking/backend/node_modules/amqplib/node_modules/bluebird/js/release/async.js:138:12)
    at _drainQueue (/home/ubuntu/Desktop/easy-tracking/backend/node_modules/amqplib/node_modules/bluebird/js/release/async.js:131:9)
    at Async._drainQueues (/home/ubuntu/Desktop/easy-tracking/backend/node_modules/amqplib/node_modules/bluebird/js/release/async.js:147:5)
    at Immediate.Async.drainQueues (/home/ubuntu/Desktop/easy-tracking/backend/node_modules/amqplib/node_modules/bluebird/js/release/async.js:17:14)
    at processImmediate (timers.js:632:19)
(node:18911) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 2)
(node:18911) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
      1) shouldnt connect to RabbitMQ service successfully with the wrong host.


1) RabbitMQMailer component.
       RabbitMQMailer configuration information.
         shouldnt connect to RabbitMQ service successfully with the wrong host.:
     Error: Timeout of 2000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/home/ubuntu/Desktop/easy-tracking/backend/src/components/rabbitmqmailer/rabbitmqmailer.test.js)

Answer 1

You need to reject the Promise.

connect(host) {
    return new Promise((resolve, reject) => {
      amqp.connect(host)
        .then((conn) => resolve(conn))
        .catch((err) => reject(new Error(err));
   });
}

And the test

it('shouldnt connect to RabbitMQ service successfully with the wrong host.', () => {
  return rabbitmqmailer.connect('amqp://wronghost')
    .then(() => { assert.fail('was not supposed to succeed'); })
    .catch((err) => { expect(err).to.be.an.instanceof(Error); })
})

Answer 2

Finally I found the way to test it

it('shouldnt connect to RabbitMQ service successfully with the wrong host.', (done) => {
      (async () => {
        try {
          await rabbitmqmailer.connect('amqp://wronghost');
        } catch (error) {
          chai.assert.typeOf(error, 'error');
        } finally {
          done();
        }
      })();
    });

But there's some strange issue, if I change the type like a 'string' for example, it tells me:

(node:26053) UnhandledPromiseRejectionWarning: AssertionError: expected [Error: Error: getaddrinfo EAI_AGAIN wronghost wronghost:5672] to be a string

But ! the test passes successfully :

 ✓ shouldnt connect to RabbitMQ service successfully with the wrong host.

I don't know why it's happen but it works anyway, thanks for the help.

Answer 3

You are not properly failing. You forgot about the reject. Do this instead:

connect(host) {
    return new Promise((resolve, reject) => {
      amqp.connect(host)
        .then((conn) => {
          resolve(conn);
        })
        .catch((err) => {
          reject(new Error(err)); // Pass the error to reject
        });
    });
  }

In your test, use instanceof to match the Error that is returned:

it('shouldnt connect to RabbitMQ service successfully with the wrong host.', async () => {
      const result = await rabbitmqmailer.connect('amqp://wronghost');
      expect(result).to.be.an.instanceof(Error);
    });

---

Also I don't know what you are using for testing, but if it is jest, then this link might help you properly test the promise.

EDIT: Actually nvm. I see you are using Chai

Answer 4

You usually want your tests to be isolated. I would recommend mocking your amqp object and expect that the connect method is being called.

It's important that you try and understand the real connect method before designing the mock

You can use a mocking framework like https://sinonjs.org/