Testing Node API with Mocha & Chai
Tags: testing, javascript, node, tutorial
Published: 2019-08-22 06:00:29

### What is Mocha? 
[Mocha](https://mochajs.org) is a feature-rich JavaScript test framework running on Node.js and in the browser, making asynchronous testing simple and fun.

- Synchronous Test Example
```js
it('two plus two is four', () => {
    expect(2 + 2).to.equals(4);
  });
```

- Asyncronous Test Code
```js
it("adds 2 numbers", (done) => {
   // perform asynchronous actions
   // write tests
    done(); // call the done function after test.
  });
```

### What is Chai?
[Chai](https://www.chaijs.com) 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:

- **[Should](https://www.chaijs.com/guide/styles/#should)**
```js
chai.should();
foo.should.be.a('string'); 
foo.should.equal('bar');
foo.should.have.lengthOf(3);
tea.should.have.property('flavors').with.lengthOf(3);
```

- **[Expect](https://www.chaijs.com/guide/styles/#expect)**
```js
var expect = chai.expect;  
expect(foo).to.be.a('string'); 
expect(foo).to.equal('bar'); 
expect(foo).to.have.lengthOf(3); expect(tea).to.have.property('flavors').with.lengthOf(3);
```

- **[Assert](https://www.chaijs.com/guide/styles/#assert)**
```js
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.
```js
const express = require("express");

const app = express();

app.use(express.json());

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;
  };
  res.json({
    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.
```json
"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](https://mochajs.org/#the-test-directory)

Then add code below 
```js
const app = require("../app");
const chai = require("chai");
const chaiHttp = require("chai-http");

const { expect } = chai;
chai.use(chaiHttp);
describe("Server!", () => {
  it("welcomes user to the api", done => {
    chai
      .request(app)
      .get("/")
      .end((err, res) => {
        expect(res).to.have.status(200);
        expect(res.body.status).to.equals("success");
        expect(res.body.message).to.equals("Welcome To Testing API");
        done();
      });
  });

  it("adds 2 numbers", done => {
    chai
      .request(app)
      .post("/add")
      .send({ num1: 5, num2: 5 })
      .end((err, res) => {
        expect(res).to.have.status(200);
        expect(res.body.status).to.equals("success");
        expect(res.body.result).to.equals(10);
        done();
      });
  });
});

```
At this point, your folder structure should look like the image below
![Folder Structure](https://thepracticaldev.s3.amazonaws.com/i/bsb8hfofzkqr9m8fqkkx.png)

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](https://thepracticaldev.s3.amazonaws.com/i/jmx31vt0krx9odxyrbff.png)

...and if the test fails, an error response on your terminal like the example shown below
![Error Test](https://thepracticaldev.s3.amazonaws.com/i/7dy3lxnj52d9inm11i7u.png)



> Find the code used in this project on [Github](https://github.com/Easybuoy/node-api-testing)
Find more information on Mocha [here](https://mochajs.org/#getting-started)
Find more information on Chai [here](https://www.chaijs.com/guide)



### Conclusion
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.