Mock dependencies with Mocha and Typescript

Question

I have a typescript project which uses mocha. Let's say we have two modules as follows.

// http.ts
export class Http {
}

// app.ts
import Http from './http';

export class App {

}

How could I mock the Http module when I'm testing the App?

The test is executed through the npm script as below.

"test": "cross-env NODE_ENV=test ./node_modules/mocha/bin/mocha",

And the mocha options (mocha.opts) looks like below.

test/setup.ts
--compilers ts:ts-node/register
--compilers tsx:ts-node/register
./src/**/*.spec.ts

Answer 1

ts-mock-imports gives you run time control over your imports and maintains type safety.

in app.spec.ts

import * as httpModule from 'http';
import { App } from '../src/app';
import { ImportMock } from 'ts-mock-imports';

const httpMock = ImportMock.mockClass(httpModule, 'Http');

const app = new App(); // App now uses a fake version of the Http class

Now you can control how the Http module behaves in your tests.

Mock the response to a get:

httpMock.mock('get', { data: true });

const response = app.makeGetRequest(); // returns { data: true }

Answer 2

The import statement in typescript is compiled to require. You can use proxyquire to mock any dependencies in your tests