Testing an Express.js API with Vitest

Learn how to create super fast tests with Vitest and Supertest for your Express.js API.

April 11, 2024

💻 Vitest 💻 Express.js 💻 Supertest

Step 1: Express set up

Init the repository

Create a new directory for your project and navigate into it:

mkdir my-express-app && cd my-express-app

Then, initialize a new Node.js project:

npm init -y

Next, install the dependencies:

npm install express vitest @vitest/ui supertest dotenv

Create API files

Create a new file and add our routes so you can export them and start the server with those routes and also be able to test them:

touch root.js

Add:

import express from "express";
const app = express();

app.get("/api/products", (req, res) => {
  res.status(200).json([
    {
      id: 1,
      name: "iPhone",
    },
    {
      id: 2,
      name: "MacBook Pro",
    },
  ]);
});

export { app };

Create the file that will initialize the server, we can run it with the “node app.js” command:

touch app.js

import { app } from "./root.js";

import dotenv from "dotenv";

dotenv.config();
const port = process.env.PORT || 3000;

app.listen(port, () => {
  console.log(`⚡ Server listening on port \x1b[33m${port}\x1b[37m`);
});

Update package.json to be able to use ECMAScript modules. Your file should look like this:

{
  "name": "my-express-app",
  "version": "1.0.0",
  "type": "module",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "@vitest/ui": "^1.4.0",
    "dotenv": "^16.4.5",
    "express": "^4.19.1",
    "supertest": "^6.3.4",
    "vitest": "^1.4.0"
  }
}

Now you can test your API using the following command!

node app.js

Step 2: Vitest set up

Create Test files

Create the file that will be read by vitest and write the test:

touch index.test.js

Add:

import { test, beforeEach, afterEach } from "vitest";
import { app } from "./root.js";

import request from "supertest";

let server;

beforeEach(() => {
  server = app.listen();
});

afterEach(() => {
  server.close();
});

test("GET /api/products", async ({ expect }) => {
  const response = await request(server).get("/api/products");

  expect(response.statusCode).toBe(200);
  server.close();
});

Step 3: Test your API!

To run the test execute:

npx vitest

You got it!

npx vitest

You can make this process easier by modifying the package.json scripts like this:

"scripts": {
  "test": "vitest"
},