Testing

Let’s go through Node.js testing systematically, covering unit, integration, mocking, and TDD workflows.

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1️⃣ Why Testing in Node.js?

• Ensures code correctness and stability

• Helps catch bugs early

• Makes refactoring safer

• Critical for production-ready APIs

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2️⃣ Unit Testing

• Focuses on testing individual functions or modules in isolation.

• Common frameworks: Jest, Mocha/Chai

a) Jest Example

npm install --save-dev jest

// math.js
function add(a, b) {
  return a + b;
}
module.exports = add;
 
// math.test.js
const add = require("./math");
 
test("adds 2 + 3 to equal 5", () => {
  expect(add(2, 3)).toBe(5);
});

• Run: npx jest

• Features:

  • Assertions (toBe, toEqual, toHaveBeenCalled)

  • Snapshot testing

  • Mock functions

b) Mocha + Chai Example

npm install --save-dev mocha chai

const { expect } = require("chai");
const add = require("./math");
 
describe("add()", () => {
  it("should return sum of two numbers", () => {
    expect(add(2, 3)).to.equal(5);
  });
});

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3️⃣ Integration Testing

• Tests how multiple modules work together, e.g., API endpoints.

• Tool: Supertest (works with Express apps)

Example

npm install --save-dev supertest

const request = require("supertest");
const express = require("express");
 
const app = express();
app.get("/hello", (req, res) => res.json({ msg: "Hello World" }));
 
describe("GET /hello", () => {
  it("responds with JSON", async () => {
    const res = await request(app).get("/hello");
    expect(res.statusCode).toBe(200);
    expect(res.body.msg).toBe("Hello World");
  });
});

• Simulates real HTTP requests without starting the server

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4️⃣ Mocking/Stubbing Databases

• Avoid hitting real databases during tests → use mocks or in-memory DBs

a) Jest Mock Example

const User = require("./models/User");
 
jest.mock("./models/User");
 
test("should call User.find", async () => {
  User.find.mockResolvedValue([{ name: "Tyson" }]);
  const users = await User.find();
  expect(users[0].name).toBe("Tyson");
});

b) In-memory DB

• MongoDB Memory Server → test MongoDB queries without real DB

npm install --save-dev mongodb-memory-server

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5️⃣ Test-Driven Development (TDD) Workflow

1. Write a failing test for a new feature

2. Implement the feature to make the test pass

3. Refactor code while keeping tests green

4. Repeat

Benefits

• Forces clear API design

• Reduces bugs in production

• Improves code modularity and maintainability

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6️⃣ Key Takeaways

Testing Type	Tools	Focus
Unit Test	Jest, Mocha/Chai	Single functions/modules
Integration Test	Supertest, Jest	API endpoints, module interactions
Mocking/Stubbing	Jest mocks, sinon	Replace DB / dependencies in tests
TDD	Workflow	Write tests first → code → refactor

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If you want, I can next cover Node.js production best practices, combining performance, security, logging, monitoring, and deployment for real-world applications.

Do you want me to do that?