Testing - lesson 2 | HackIndia Skills

Testing - lesson 2 | HackIndia Skills | HackIndia

Example

Example unit test

Here is a small JavaScript example using Vitest. The function calculates a simple platform fee in rupees.

The test has three parts: arrange the input, act by calling the function, and assert the expected output.

// src/calculateFee.js
export function calculateFee(amount) {
  if (amount <= 0) return 0;
  return Math.ceil(amount * 0.02);
}

// src/calculateFee.test.js
import { describe, it, expect } from 'vitest';
import { calculateFee } from './calculateFee.js';

describe('calculateFee', () => {
  it('returns 2 percent fee rounded up', () => {
    // arrange
    const amount = 101;

    // act
    const fee = calculateFee(amount);

    // assert
    expect(fee).toBe(3);
  });

  it('returns zero for zero or negative amounts', () => {
    expect(calculateFee(0)).toBe(0);
    expect(calculateFee(-50)).toBe(0);
  });
});

Your to-do

Run it locally

Do each one yourself, then tap it to tick it off. The ticks are only a checklist for you: they are not marked or scored.

Install Vitest if your JavaScript project does not already have a test runner.
Add a test script to package.json if it is missing.
Run the test command from your project root.
Read the failure message before changing code. It usually says what value was expected and what value was received.

0 of 4 done

npm install -D vitest

// package.json
{
  "scripts": {
    "test": "vitest run"
  }
}

npm test

Tip

Name tests plainly

Write the test name like a sentence: returns zero for negative amounts. A recruiter should understand the behaviour without opening the function.

If you use AI to draft tests, ask it for cases first, not code first. Then check that every case matches your actual product rules.

Prompt you can use:
I have this function. Suggest 5 useful unit test cases. Include normal cases and edge cases. Do not write code yet.

Then paste your function.

Your to-do

Do this now

Do each one yourself, then tap it to tick it off. The ticks are only a checklist for you: they are not marked or scored.

Find one pure function in your current project or create one from existing logic.
Write one test for the normal case and one test for an edge case.
Run the test locally until it passes.
Commit the function and test file together with a clear message.

0 of 4 done

git add src/calculateFee.js src/calculateFee.test.js package.json package-lock.json
git commit -m "Add unit test for fee calculation"

Write your first unit test

What you test here

One idea

Pick a function