End-to-End Backend Testing Setup (Jest + Supertest + Mongo)

[abhishek-nexgen-dev]

Our backend currently lacks a standardized, production-grade testing system.
To ensure reliability, scalability, and safe refactoring, we will implement a full testing architecture using:

• Jest → Test runner
• Supertest → API testing
• Mongo Memory Server / Test DB → Isolated database

This setup will support:

• Unit tests (functions/services)
• Integration tests (modules + DB)
• API tests (routes + auth)
• CI/CD validation

---

🎯 Objectives

• Establish a scalable testing architecture
• Enable testing for all backend layers
• Ensure isolation (no real DB pollution)
• Enforce quality via CI/CD

---

⚙️ Implementation Tasks

---

1️⃣ Install Dependencies

npm install -D jest ts-jest @types/jest supertest mongodb-memory-server

---

2️⃣ Configure Jest

📄 jest.config.ts

export default {
  preset: "ts-jest",
  testEnvironment: "node",
  testMatch: ["**/tests/**/*.test.ts"],
  moduleFileExtensions: ["ts", "js"],
  clearMocks: true,
  setupFilesAfterEnv: ["<rootDir>/tests/setup.ts"],
};

---

3️⃣ Setup Test Environment

📄 tests/setup.ts

import mongoose from "mongoose";
import { MongoMemoryServer } from "mongodb-memory-server";

let mongo: MongoMemoryServer;

beforeAll(async () => {
  mongo = await MongoMemoryServer.create();
  const uri = mongo.getUri();
  await mongoose.connect(uri);
});

afterEach(async () => {
  const collections = mongoose.connection.collections;
  for (const key in collections) {
    await collections[key].deleteMany({});
  }
});

afterAll(async () => {
  await mongoose.connection.close();
  await mongo.stop();
});

---

4️⃣ Update Scripts

📄 package.json

{
  "scripts": {
    "test": "jest",
    "test:watch": "jest --watch",
    "test:coverage": "jest --coverage"
  }
}

---

📁 Folder Structure

src/
 ├── controllers/
 ├── services/
 ├── models/
 ├── routes/
 ├── utils/

tests/
 ├── unit/
 ├── integration/
 ├── api/
 ├── setup.ts

---

🧪 Test Types & Examples

---

✅ 1. Unit Test (Functions)

📄 tests/unit/math.test.ts

import { describe, test, expect } from "@jest/globals";
import { square } from "../../src/utils/math";

describe("Math Utils", () => {
  test("square should return correct value", () => {
    expect(square(4)).toBe(16);
  });
});

---

✅ 2. Service Test (Business Logic)

import { createUser } from "../../src/services/user.service";

test("should create user", async () => {
  const user = await createUser({ email: "test@test.com", password: "123456" });
  expect(user.email).toBe("test@test.com");
});

---

✅ 3. API Test (Supertest)

📄 tests/api/auth.test.ts

import request from "supertest";
import app from "../../src/app";

describe("Auth API", () => {

  test("should register user", async () => {
    const res = await request(app)
      .post("/api/auth/register")
      .send({
        email: "test@test.com",
        password: "123456"
      });

    expect(res.status).toBe(201);
  });

});

---

✅ 4. Auth Test (JWT / Protected Route)

test("should access protected route", async () => {
  const login = await request(app)
    .post("/api/auth/login")
    .send({ email: "test@test.com", password: "123456" });

  const token = login.body.token;

  const res = await request(app)
    .get("/api/protected")
    .set("Authorization", `Bearer ${token}`);

  expect(res.status).toBe(200);
});

---

🧠 Testing Guidelines

✅ MUST TEST

• Utility functions
• Services (business logic)
• Controllers
• Authentication flows
• Critical APIs
• Bug fixes (regression tests)

---

⚠️ OPTIONAL

• Simple DTOs
• Non-critical helpers

---

❌ DO NOT TEST

• Third-party libraries
• Framework internals
• Trivial code

---

🔐 Best Practices

• Use test DB only (never production DB)
• Reset DB after each test
• Keep tests deterministic
• Avoid shared state
• Use mocks when needed

---

🚀 CI/CD Integration

📄 .github/workflows/test.yml

name: Run Tests

on:
  push:
    branches: [main]
  pull_request:

jobs:
  test:
    runs-on: ubuntu-latest

    steps:
      - uses: actions/checkout@v3
      - uses: actions/setup-node@v3
        with:
          node-version: 18

      - run: npm install
      - run: npm test

---

📊 Coverage Goal

• Minimum coverage: 80%

• Focus on:

  • services
  • controllers
  • critical flows

---

✅ Acceptance Criteria

• Jest configured
• Test DB working
• Unit tests added
• API tests added
• Auth tested
• Tests pass locally
• CI pipeline runs tests
• Coverage report generated

---

🔥 Priority

High — required before scaling backend features

---

🧠 Engineering Rule

• No test → No merge ❌
• Every bug → must include test ✅
• Tests must run in CI before deploy

---

⚡ Final Outcome

After this issue:

• Backend becomes testable, reliable, scalable
• Safe refactoring enabled
• Production bugs reduced significantly