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Testing Node API with Mocha & Chai

easybuoy profile image Ekunola Ezekiel Updated on ・3 min read

What is Mocha?

Mocha is a feature-rich JavaScript test framework running on Node.js and in the browser, making asynchronous testing simple and fun.

  • Synchronous Test Example
it('two plus two is four', () => {
    expect(2 + 2).to.equals(4);
  • Asyncronous Test Code
it("adds 2 numbers", (done) => {
   // perform asynchronous actions
   // write tests
    done(); // call the done function after test.

What is Chai?

Chai is a BDD (Behaviour-Driven Development) / TDD (Test-Driven Development) assertion library for nodejs and the browser that can be delightfully paired with any javascript testing framework.

Assertion Types

Chai has several interfaces from which developers can choose from. They are:

var expect = chai.expect;  
expect(foo).to.have.lengthOf(3); expect(tea).to.have.property('flavors').with.lengthOf(3);
var assert = chai.assert;  
assert.typeOf(foo, 'string'); 
assert.equal(foo, 'bar'); 
assert.lengthOf(foo, 3);
assert.property(tea, 'flavors'); 
assert.lengthOf(tea.flavors, 3);

Server Test

Now, I would be taking us through the process of setting up a basic Node API and writing tests for it.

First thing is to create our project folder and initialize it with npm to generate the package.json file.

npm init -y

Install dependencies by running the commands below on your terminal

npm i express --save
npm i mocha chai chai-http --save-dev

Setup Server

Create an app.js file in the root of your project and add code below to create a server with express and also endpoints that we would be testing.

const express = require("express");

const app = express();


app.get("/", (req, res) => {
  res.json({ status: "success", message: "Welcome To Testing API" });

app.post("/add", (req, res) => {
  const { num1, num2 } = req.body;
  const add = (num1, num2) => {
    return num1 + num2;
    status: "success",
    result: "Welcome To Testing API",
    result: add(num1, num2)

const PORT = process.env.PORT || 3000;

app.listen(PORT, () => console.log(`App listening on port ${PORT}`));

module.exports = app;

Setup Scripts

Add test script to package.json file.

"scripts": {
    "test": "mocha"

Write Tests

Create a test directory in your project, and then create an app.test.js file inside the test directory created.

Note: The reason we're adding our tests to the test directory is that mocha searches for a test directory in your project by default, although this can be configured to suit your style. Find more here

Then add code below

const app = require("../app");
const chai = require("chai");
const chaiHttp = require("chai-http");

const { expect } = chai;
describe("Server!", () => {
  it("welcomes user to the api", done => {
      .end((err, res) => {
        expect(res.body.message).to.equals("Welcome To Testing API");

  it("adds 2 numbers", done => {
      .send({ num1: 5, num2: 5 })
      .end((err, res) => {

At this point, your folder structure should look like the image below
Folder Structure

To run the test, run the command below on your terminal.

npm test

Once the test is run, if the test passes, you should get a successful response on your terminal like the example shown below
Success Test

...and if the test fails, an error response on your terminal like the example shown below
Error Test

Find the code used in this project on Github
Find more information on Mocha here
Find more information on Chai here


In this article, we have been able to look at setting up testing with Mocha and Chai and also writing tests for our Node API. I would be improving on this article and project to integrate a Continuous Integration tool called Travis-CI.

If you have any questions or feedback about this article, feel free to leave a comment.
Thanks for reading.

Posted on Aug 22 '19 by:

easybuoy profile

Ekunola Ezekiel


Full-Stack Web Application developer with a passion for web technologies.


markdown guide

How can i store value from one API call & use it in next ?


You can nest API calls, an example below

        email: 'example@gmail.com', password: '123456',
      .end((err, res) => {
        const { token } = res.body.data;
        storeownertoken = token;

            email: 'example2@gmail.com', password: '123456',
          .end((err2, res2) => {
            storeattendanttoken = res2.body.data.token;
                email: 'example31@gmail.com', password: '123456',
              .end((err3, res3) => {
                undefinedtypetoken = res3.body.data.token;

I hope it makes sense?


Hi! Thank you For responding, but it is still not working for me, the variable I am storing from the first API call turns out to be null when accessed in 2nd API call.
My Scenario: 1st Post call - Get an access token which I am successfully able to capture , 2nd Post call - Use this access token to view authenticated data.

Yeah, your process seems right, not quite sure why you're getting null. Can I see a screenshot of the code?

This is what i have.. i am not sure what I am doing wrong.
Here I do get the token from Authurl but when I access it for next call .. i don't get the token hence it fails
---- Code --

var authtoken ="";
describe('/Get Welcome Message', () => {
it('Generate Auth token', (done) => {
.set('_format', 'json')
.end((err, res) => {
authToken = res.text.slice(10,-21);
console.log("authToken : "+JSON.stringify(res.text.slice(10,-21)));
.set('componentName', 'banner')
.set('_format', 'json')
.end((err, res) => {
console.log("Token : "+authtoken);
console.log("Response : "+JSON.stringify(res));
----- end ---

Okay, have you tried logging the error you're getting on the second API call to see what the error is?

Yes ...when i log the err .. its null.
But the response shows a 401 , which is an authentication error. Also I print the auth token which turns out to be null. Hence I believe the token is not getting passed to the 2nd API .

That's wired, let's try making the first request in a before hook, and then use the token where needed.

You can search here and see an implementation for hooks: mochajs.org/

Hi! I have the code working now but the before/before each didn't seem to work as expected. I realized I was making a mistake while parsing the JSON response.
Thanks a lot for helping.


Great tutorial! What icons are you using on the screenshot of the file structure?


Thanks, John. I installed a vs code extension called Material Icon Theme.


Thanks for this, i really love the analogy you used in explaining it


Hi! Ez.

Do you provide test to check if an HTML element is DOM injected after a GET ?

It would be great to read you about that ;)