How do I unit test HTTP requests?

Question

As the title asks how do I test HTTP requests with Mocha and Chai?

I've recently started learning unit testing and I'm still getting confused with certain aspects of testing. I can get by fine testing methods that return a value but I'm confused on how to test methods that make HTTP/IO requests.

For example I have the following code:

module.exports = someRequest => new Promise((resolve, reject) => 
    http.get('http://google.com', resp => {
        if(resp.headers['content-type'] !== 200) {
            reject(new Error('Failed to connect to Google'));
        }
        resolve('Connected to Google');
    })
);

I want to test 2 cases:

1. The request to Google succeed
2. The request to Google failed

Do I have to mock these requests and if so what's the purpose of mocking a method that is intended to make a HTTP request?

Answer 1

How about mocking http.get with something like that ?

const createHttpGetMock = (expectedStatus) => {
  return httpGetMock = (address) => {
    return new Promise((resolve, reject) => {
      resolve({
        status: expectedStatus,
        headers: {
          // ... headers
        },
        // mock response
      })
    })
  }
}

Then your test could look like this :

describe("Google request", () => {
  it("Resolves when google responds", async () => {
    const httpSuccessMock = createHttpGetMock(200);
    // Inject your mock inside your request function here, using your favorite lib

    const message = await fetchGoogle();
    assert.equals(message, 'Connected to Google');
  })

  it("Rejects when google responds with error", async () => {
    const httpSuccessMock = createHttpGetMock(500);
    // Inject your mock inside your request function here, using your favorite lib

    const message = await fetchGoogle();
    assert.equals(message, 'Failed to connect to Google');
  })
});

This would fulfill the basic contract of a good unit test : regardless of external modules and dependencies, it ensures the module you're currently testing has the correct behaviour in each possible case.

Answer 2

Here is an example of test with mocha and chai. We also need sinon to stub the http library.

http://sinonjs.org/releases/v1.17.7/stubs/

// test.js

const chai = require('chai');
const expect = chai.expect;
const sinon = require('sinon');
const http = require('http');

const someRequest = require('./index');

describe('some request test', function() {
  let httpGetStub;

  beforeEach(function() {
    httpGetStub = sinon.stub(http, 'get'); // stub http so we can change the response
  });

  afterEach(function() {
    httpGetStub.restore();
  });

  it('responses with success message', function() {
    httpGetStub.yields({ headers: { 'content-type': 200 }}); // use yields for callback based function like http.get
    return someRequest().then(res => { 
      expect(res).to.equal('Connected to Google');      
    });
  });

  it('rejects with error message', function() {
    httpGetStub.yields({ headers: { 'content-type': 400 }});
    return someRequest().catch(err => { 
      expect(err.message).to.equal('Failed to connect to Google');      
    });
  });
})

Hope it helps.