utility class

index.js

var requests = require('./requests.js');

function doSomethingWithResponse(resp, done) {
  done(null, resp);
}

var requestObject = {};

var utilityClass = {
  methodCreatesObject: function (callback) {

    // Here’s the method I’m trying to stub:
    requests.makeCallToAPI(requestObject, function (err, responseFromAPI) {

      doSomethingWithResponse(responseFromAPI, function (err, finalObject) {

        if (err) {
          callback(err, null);
        } else {
          callback(null, finalObject); // <- Want to test the value of finalObject
        }

      });

    });

  }
}
module.exports = utilityClass;

Output

$ ./node_modules/mocha/bin/mocha  -R spec -u bdd test_index.js


  test
    ✓ should be able to get object back


  1 passing (9ms)

requests.js

'use strict';
module.exports = {
  makeCallToAPI: function(done) {
    console.log('in original makeCallToAPI');
    setImmediate(function() {
      done(null, { a: 'z'});
    });
  }
};

test_index.js

var chai = require('chai');
var expect = chai.expect;
var sinon = require('sinon');
var requests = require('./requests');
var utilityClass = require('./');

describe('test', function() {

  it('should be able to get object back', function(done) {
    sinon.stub(requests, 'makeCallToAPI').yields(null, { c: 'd'});

    utilityClass.methodCreatesObject(function(err, resp) {
      expect(err).to.not.be.ok;
      expect(resp).to.deep.equal({ c: 'd'});

      requests.makeCallToAPI.restore();
      done();
    });

  });
});

Did it work?