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Unit Test Writing Framework

Write comprehensive unit tests using AAA pattern (Arrange, Act, Assert) with edge cases, mocks, and coverage targets.

Updated June 2026

unit-test-writing-framework.txt

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You are a software engineer who writes exemplary unit tests. Your principles: (1) tests document behavior — the test name should say what the code does, (2) Arrange-Act-Assert — clear structure in every test, (3) each test tests ONE thing — if it fails, you know exactly what broke, (4) tests must be fast and independent — no dependency on order or shared state, (5) test behavior, not implementation — tests should not break when you refactor.

Create unit tests for:

**Language:** [e.g.: TypeScript, Python, Go, Java]
**Test framework:** [e.g.: Jest, Vitest, pytest, Go testing, JUnit]
**Code to test:** [paste the function/class/module]
**Context:** [what this code does in the system]
**External dependencies:** [database, APIs, filesystem — what needs to be mocked]
**Known special cases:** [edge cases you know exist]

Deliver:

**1. Code analysis** - What it does, inputs, outputs, side effects
**2. Scenario matrix** - Table with scenario, input, output, type
**3. Complete tests** - Code organized by describe/context
**4. Error tests** - Null input, wrong types, failing dependency
**5. Coverage achieved** - Lines and branches covered
**6. Maintenance tips** - How to maintain the tests as the code evolves

When to Use

When implementing tests for the first time in a project

To standardize how the team writes tests

When test coverage is low or tests are fragile

Before refactoring critical code

How to Use This Prompt

Copy the prompt below into Claude or ChatGPT

Paste the function or module you want to test

Receive the complete tests with explanations

Implement and run in your test runner

Example Input

Language: TypeScript
Framework: Jest
Code: Function calculateDiscount(price, couponCode, userTier)
- Applies discount based on coupon + user tier
- Premium = 10% extra, VIP = 20% extra
- Coupon can be percentage or fixed value
- Minimum final price is R$1.00

Expected Output

describe('calculateDiscount', () => {
  describe('without coupon', () => {
    it('returns original price for regular user without coupon', () => {
      const result = calculateDiscount(100, null, 'regular');
      expect(result).toBe(100);
    });

    it('applies 10% discount for premium user', () => {
      const result = calculateDiscount(100, null, 'premium');
      expect(result).toBe(90);
    });

    it('applies 20% discount for VIP user', () => {
      const result = calculateDiscount(100, null, 'vip');
      expect(result).toBe(80);
    });
  });

  describe('edge cases', () => {
    it('never returns value less than R$1.00', () => {
      const result = calculateDiscount(5, 'SAVE99', 'vip');
      expect(result).toBe(1);
    });

    it('throws error for negative price', () => {
      expect(() => calculateDiscount(-10, null, 'regular'))
        .toThrow('Price must be positive');
    });
  });
});

Unit Test Writing Framework

When to Use

How to Use This Prompt

Example Input

Expected Output

Ready to use this prompt?