How to mock a function in another function nodejs

Question

Trying to write a unittest for the below module in /utility/sqsThing.js. However I'm having diffuculty mocking the sqs.sendMessage method. Anyone know how I should go about this. I'm using the sinon library, and mocha for running the tests.

The function that I'm trying to unittest utility/sqsThing.js:

const AWS = require('aws-sdk');
AWS.config.update({ region: 'us-east-1' });
const sqs = new AWS.SQS({ apiVersion: '2012-11-05' });
const outputQueURL = 'https:awsUrl';

const SQSOutputSender = (results) => {
  const params = {
    MessageBody: JSON.stringify(results),
    QueueUrl: outputQueURL,
  };
  // Method that I want to mock
  sqs.sendMessage(params, function (err, data) {
    if (err) {
      console.log('Error');
    } else {
      console.log('Success', data.MessageId);
    }
  });
};

My attempt at mocking the sqs.sendMessage method in a unittest sqsThingTest.js:

const sqsOutputResultSender = require('../utility/sqsThing');
const AWS = require('aws-sdk');
const sqs = new AWS.SQS({ apiVersion: '2012-11-05' });

const mochaccino = require('mochaccino');

const { expect } = mochaccino;
const sinon = require('sinon');


describe('SQS thing test', function() {
    beforeEach(function () {
        sinon.stub(sqs, 'sendMessage').callsFake( function() { return 'test' });
    });

    afterEach(function () {
        sqs.sendMessage.restore();
    });

  it('sqsOutputResultSender.SQSOutputSender', function() {
    // Where the mock substitution should occur
    const a = sqsOutputResultSender.SQSOutputSender('a');
    expect(a).toEqual('test');
  })
});

Running this unittest with mocha tests/unit/sqsThingTest.js however I get: AssertionError: expected undefined to deeply equal 'test'. info: Error AccessDenied: Access to the resource https://sqs.us-east-1.amazonaws.com/ is denied..

It looks like the mock did not replace the aws api call. Anyone know how I can mock sqs.SendMessage in my test?

@JonathanNewton Tried sinon.stub(sqs.prototype, 'sendMessage').callsFake( function() { return 'test' }). That gives me this error: Error: Trying to stub property 'sendMessage' of undefined — dredbound
– dredbound, Commented Nov 16, 2018 at 16:13

Shan Eapen Koshy · Accepted Answer · 2020-10-14 02:30:14Z

1

You could use rewire js it is a library that lets you inject mocked properties into your module you want to test.

Your require statement would look something like this:

var rewire = require("rewire");
var sqsOutputResultSender = rewire('../utility/sqsThing');

Rewire will allow you to mock everything in the top-level scope of you sqsThing.js file.

Also you need to return the value of sqs.sendMessage this will remove the issue expected undefined to deeply equal 'test'

Your original file would look the same just with a return statement.

//utility/sqsThing.js
const AWS = require('aws-sdk');
AWS.config.update({ region: 'us-east-1' });
const sqs = new AWS.SQS({ apiVersion: '2012-11-05' });
const outputQueURL = 'https:awsUrl';

const SQSOutputSender = (results) => {
  const params = {
    MessageBody: JSON.stringify(results),
    QueueUrl: outputQueURL,
  };
  // Method that I want to mock
  return sqs.sendMessage(params, function (err, data) {
    if (err) {
      console.log('Error');
    } else {
      console.log('Success', data.MessageId);
    }
  });
};

You would then write your unit test as follows:

//sqsThingTest.js
var rewire = require("rewire");
var sqsOutputResultSender = rewire('../utility/sqsThing');
const mochaccino = require('mochaccino');
const { expect } = mochaccino;
const sinon = require('sinon');

describe('SQS thing test', function() {
    beforeEach(function () {
        sqsOutputResultSender.__set__("sqs", {
            sendMessage: function() { return 'test' }
        });
    });

  it('sqsOutputResultSender.SQSOutputSender', function() {
    // Where the mock substitution should occur
    const a = sqsOutputResultSender.SQSOutputSender('a');
    expect(a).toEqual('test');
  })
});

This example returns an object with a property of sendMessage but this could be replaces with a spy.

Rewire Docs

edited Oct 14, 2020 at 2:30

Shan Eapen Koshy

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answered Nov 19, 2018 at 16:08

Jonathan Newton

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2 Comments

dredbound Over a year ago

Works for me. Just had to change myModule to sqsOutputResultSender.

Jonathan Newton Over a year ago

@dredbound fixed

Jonathan Newton · Accepted Answer · 2018-11-16 16:19:10Z

1

Try moving the declaration of sqsOutputResultSender after you have stubbed the sendmessage function

    var sqsOutputResultSender;
    const AWS = require('aws-sdk');
    const sqs = new AWS.SQS({ apiVersion: '2012-11-05' });

    const mochaccino = require('mochaccino');

    const { expect } = mochaccino;
    const sinon = require('sinon');


    describe('SQS thing test', function() {
        beforeEach(function () {
            sinon.stub(sqs, 'sendMessage').callsFake( function() { return 'test' });
            sqsOutputResultSender = require('../utility/sqsThing');
        });

        afterEach(function () {
            sqs.sendMessage.restore();
        });

      it('sqsOutputResultSender.SQSOutputSender', function() {
        // Where the mock substitution should occur
        const a = sqsOutputResultSender.SQSOutputSender('a');
        expect(a).toEqual('test');
      })
    });

answered Nov 16, 2018 at 16:19

Jonathan Newton

8587 silver badges19 bronze badges

14 Comments

dredbound Over a year ago

No, still gives me the same AssertionError: expected undefined to deeply equal 'test'. and info: Error AccessDenied: Access to the resource https://sqs.us-east-1.amazonaws.com/ is denied.

Jonathan Newton Over a year ago

Could you move the call to sqs.sendMessage inside another function?

dredbound Over a year ago

I could, but I'd still need to mock it in order to test that function wherever I move it.

Jonathan Newton Over a year ago

I'm not sure why you can access it but here is a suggestion: Gist then your stub would look something like this ` sinon.stub(sqsOutputResultSender, 'sendMessage').callsFake( function() { return 'test' });`

dredbound Over a year ago

Running that is still returning the same AssertionError: expected undefined to deeply equal 'test'. It's not replacing the function with the stub. I suspect that I'm just not using sinon correctly.

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