• Init express app

npm init -y
npx tsc --init
npm install express @types/express zod

• Update tsconfig

"rootDir": "./src",
"outDir": "./dist"

• Write a simple src/index.ts file

import express from "express";
import { z } from "zod";

export const app = express();
app.use(express.json());

const sumInput = z.object({
    a: z.number(),
    b: z.number()
})

app.post("/sum", (req, res) => {
    const parsedResponse = sumInput.safeParse(req.body)

    if (!parsedResponse.success) {
        return res.status(411).json({
            message: "Incorrect inputs"
        })
    }

    const answer = parsedResponse.data.a + parsedResponse.data.b;

    res.json({
        answer
    })
});

app.get("/sum", (req, res) => {
    const parsedResponse = sumInput.safeParse({
        a: Number(req.headers["a"]),
        b: Number(req.headers["b"])
    })

    if (!parsedResponse.success) {
        return res.status(411).json({
            message: "Incorrect inputs"
        })
    }

    const answer = parsedResponse.data.a + parsedResponse.data.b;

    res.json({
        answer
    })
});

💡

We’re not doing an app.listen here. This is because we dont want the app to actually start when the tests are running. Usually you create a bin.ts file or main.ts file that imports app and actually listens on a port

• Install vitest

npm i -D vitest

• Add a simple test/index.test.ts file

import { expect, test } from 'vitest'

test('true === true', () => {
  expect(true).toBe(true)
})

• Add a script to test in package.json

"test": "vitest"

• Add supertest

npm i supertest @types/supertest

• Update test - Notice all we had to do was update the imports. vitest is highly compatible with the jest api

import {describe, expect, test, it} from 'vitest';
import request from "supertest";
import { app } from "../index"

describe("POST /sum", () => {
  it("should return the sum of two numbers", async () => {
      const res = await request(app).post("/sum").send({
        a: 1,
        b: 2
      });
      expect(res.statusCode).toBe(200);
      expect(res.body.answer).toBe(3);
    });

    it("should return 411 if no inputs are provided", async () => {
      const res = await request(app).post("/sum").send({});
      expect(res.statusCode).toBe(411);
      expect(res.body.message).toBe("Incorrect inputs");
    });

});

describe("GET /sum", () => {
  it("should return the sum of two numbers", async () => {
      const res = await request(app)
        .get("/sum")
        .set({
          a: "1",
          b: "2"
        })
        .send();
      expect(res.statusCode).toBe(200);
      expect(res.body.answer).toBe(3);
  });

  it("should return 411 if no inputs are provided", async () => {
    const res = await request(app)
      .get("/sum").send();
    expect(res.statusCode).toBe(411);
  });

});