Nodejs - Mocha, Chai multiple async testing - node.js

Question

Complete NodeJS testing noob here. Trying to individually test functions that are called through my API (meaning, rather than make an http request to a specific endpoint, which usually invokes several functions, which in turn make requests to different third party APIs, I want to test the functions themselves separately). The way they're called is I've built a class for each data source (data source = third party API), each class contains the same functions with the same exact signatures - getData and convertData, and return a callback with the results.
I've also created a module that creates many user mocks, since each user context returns different data (meaning, a user object is fed into getData, which uses certain user properties in order to determine what data should be returned).
The way I wanted to test this was to create numerous mocks, then run the functions for each. This is what I've got so far:
// Data sources to iterate over. Each is a class instance acquired through "require".
var dataSources = [
source1,
source2,
source3,
source4
];
describe('getData', function() {
this.timeout(10000);
describe('per data source,', function() {
context('standard call', function() {
// Associative array to hold the data returned, a key for each data source.
var finalResults = {};
// Iterate over all data sources
_.forEach(dataSources, function(dataSource) {
// Generate user mocks
var users = userMocks(10);
// Iterate over all users.
_.forEach(users, function (user) {
// Call each data source with each of the users.
// Numbers of calls to make - (users * data-sources), so in this case - 10*4.
dataSource.getData(user, function (err, data) {
if (err) return done(err);
// Convert the data returned to my format
dataSource.convertData(data, function (err, processedData) {
if (err) return done(err);
// Populate finalResults with converted data from each source
if (finalResults[dataSource.sourceName]) {
finalResults[dataSource.sourceName] = finalResults[dataSource.sourceName].concat(processedData);
} else {
finalResults[dataSource.sourceName] = processedData;
}
});
});
});
});
it('should return something', function(done) {
_.forEach(finalResults.keys, function(key) {
expect(finalResults[key]).to.not.be.empty;
expect(finalResults[key].length).to.be.greaterThan(0);
});
setTimeout(function() {
done();
}, 10000);
})
});
});
});
});`
This works (or at least the test passes when the query is valid, which is what I wanted), but it's cumbersome and (so very) far from elegant or effective, specifically the usage of timeout rather than using promises, async of some sort, or maybe a different alternative I'm not yet familiar with.
Since most of the resources I found (http://alanhollis.com/node-js-testing-a-node-js-api-with-mocha-async-and-should/, https://developmentnow.com/2015/02/05/make-your-node-js-api-bulletproof-how-to-test-with-mocha-chai-and-supertest/, https://justinbellamy.com/testing-async-code-with-mocha/, just to name a few) discuss direct API testing rather than specific async functions, I would love to get some input/best practices tips from more experienced Noders.

Answer 1

You need to know when bunch of asynchronous operations complete. Elegant way to test that is to use promises and promise aggregation:
Promise.all([ promise1, promise2, promise3 ]).then(function(results) {
// all my promises are fulfilled here, and results is an array of results
});
Wrap your dataSources into a promises using bluebird. You don't need to modify tested code self, bluebird provides convenience method:
var Promise = require('bluebird')
var dataSources = [
source1,
source2,
source3,
source4
].map(Promise.promisifyAll);
Use newly promisified functions to create promise for each call:
context('standard call', function() {
var finalResults = {};
var promiseOfResults = datasources.map(function(dataSource) {
var users = userMocks(10);
// Promise.all will take an array of promises and return a promise that is fulfilled then all of promises are
return Promise.all( users.map(function(user) {
// *Async functions are generated by bluebird, via Promise.promisifyAll
return dataSource.getDataAsync(user)
.then(dataSource.convertDataAsync)
.then(function(processedData) {
if (finalResults[dataSource.sourceName]) {
finalResults[dataSource.sourceName] = finalResults[dataSource.sourceName].concat(processedData);
} else {
finalResults[dataSource.sourceName] = processedData;
}
});
});
});
// promiseOfResults consists now of array of agregated promises
it('should return something', function(done) {
// Promise.all agregates all od your 'datasource' promises and is fulfilled when all of them are
// You don't need the promise result here, since you agegated finalResults yourself
return Promise.all( promiseOfResults ).then(function() {
_.forEach(finalResults.keys, function(key) {
expect(finalResults[key]).to.not.be.empty;
expect(finalResults[key].length).to.be.greaterThan(0);
});
done();
});
});
Rest of your test should use same Promise.all( promiseOfResults ), unless you need new set of results.