testing-strategies

Testing Strategies

When to use this skill

New project

define a testing strategy

Quality issues

bugs happen frequently

Before refactoring

build a safety net

CI/CD setup

automated tests Instructions Step 1: Understand the Test Pyramid /\ /E2E\ ← few (slow, expensive) /__\ / \ /Integration\ ← medium /_\ / \ / Unit Tests \ ← many (fast, inexpensive) /_______\ Ratio guide : Unit: 70% Integration: 20% E2E: 10% Step 2: Unit testing strategy Given-When-Then pattern : describe ( 'calculateDiscount' , ( ) => { it ( 'should apply 10% discount for orders over $100' , ( ) => { // Given: setup const order = { total : 150 , customerId : '123' } ; // When: perform action const discount = calculateDiscount ( order ) ; // Then: verify result expect ( discount ) . toBe ( 15 ) ; } ) ; it ( 'should not apply discount for orders under $100' , ( ) => { const order = { total : 50 , customerId : '123' } ; const discount = calculateDiscount ( order ) ; expect ( discount ) . toBe ( 0 ) ; } ) ; it ( 'should throw error for invalid order' , ( ) => { const order = { total : - 10 , customerId : '123' } ; expect ( ( ) => calculateDiscount ( order ) ) . toThrow ( 'Invalid order' ) ; } ) ; } ) ; Mocking strategy : // Mock external dependencies jest . mock ( '../services/emailService' ) ; import { sendEmail } from '../services/emailService' ; describe ( 'UserService' , ( ) => { it ( 'should send welcome email on registration' , async ( ) => { // Arrange const mockSendEmail = sendEmail as jest . MockedFunction < typeof sendEmail

; mockSendEmail . mockResolvedValueOnce ( true ) ; // Act await userService . register ( { email : 'test@example.com' , password : 'pass' } ) ; // Assert expect ( mockSendEmail ) . toHaveBeenCalledWith ( { to : 'test@example.com' , subject : 'Welcome!' , body : expect . any ( String ) } ) ; } ) ; } ) ; Step 3: Integration Testing API endpoint tests : describe ( 'POST /api/users' , ( ) => { beforeEach ( async ( ) => { await db . user . deleteMany ( ) ; // Clean DB } ) ; it ( 'should create user with valid data' , async ( ) => { const response = await request ( app ) . post ( '/api/users' ) . send ( { email : 'test@example.com' , username : 'testuser' , password : 'Password123!' } ) ; expect ( response . status ) . toBe ( 201 ) ; expect ( response . body . user ) . toMatchObject ( { email : 'test@example.com' , username : 'testuser' } ) ; // Verify it was actually saved to the DB const user = await db . user . findUnique ( { where : { email : 'test@example.com' } } ) ; expect ( user ) . toBeTruthy ( ) ; } ) ; it ( 'should reject duplicate email' , async ( ) => { // Create first user await request ( app ) . post ( '/api/users' ) . send ( { email : 'test@example.com' , username : 'user1' , password : 'Pass123!' } ) ; // Attempt duplicate const response = await request ( app ) . post ( '/api/users' ) . send ( { email : 'test@example.com' , username : 'user2' , password : 'Pass123!' } ) ; expect ( response . status ) . toBe ( 409 ) ; } ) ; } ) ; Step 4: E2E Testing (Playwright) import { test , expect } from '@playwright/test' ; test . describe ( 'User Registration Flow' , ( ) => { test ( 'should complete full registration process' , async ( { page } ) => { // 1. Visit homepage await page . goto ( 'http://localhost:3000' ) ; // 2. Click Sign Up button await page . click ( 'text=Sign Up' ) ; // 3. Fill out form await page . fill ( 'input[name="email"]' , 'test@example.com' ) ; await page . fill ( 'input[name="username"]' , 'testuser' ) ; await page . fill ( 'input[name="password"]' , 'Password123!' ) ; // 4. Submit await page . click ( 'button[type="submit"]' ) ; // 5. Confirm success message await expect ( page . locator ( 'text=Welcome' ) ) . toBeVisible ( ) ; // 6. Confirm redirect to dashboard await expect ( page ) . toHaveURL ( 'http://localhost:3000/dashboard' ) ; // 7. Confirm user info is displayed await expect ( page . locator ( 'text=testuser' ) ) . toBeVisible ( ) ; } ) ; test ( 'should show error for invalid email' , async ( { page } ) => { await page . goto ( 'http://localhost:3000/signup' ) ; await page . fill ( 'input[name="email"]' , 'invalid-email' ) ; await page . fill ( 'input[name="password"]' , 'Password123!' ) ; await page . click ( 'button[type="submit"]' ) ; await expect ( page . locator ( 'text=Invalid email' ) ) . toBeVisible ( ) ; } ) ; } ) ; Step 5: TDD (Test-Driven Development) Red-Green-Refactor Cycle : // 1. RED: write a failing test describe ( 'isPalindrome' , ( ) => { it ( 'should return true for palindrome' , ( ) => { expect ( isPalindrome ( 'racecar' ) ) . toBe ( true ) ; } ) ; } ) ; // 2. GREEN: minimal code to pass the test function isPalindrome ( str : string ) : boolean { return str === str . split ( '' ) . reverse ( ) . join ( '' ) ; } // 3. REFACTOR: improve the code function isPalindrome ( str : string ) : boolean { const cleaned = str . toLowerCase ( ) . replace ( / [ ^ a - z 0 - 9 ] / g , '' ) ; return cleaned === cleaned . split ( '' ) . reverse ( ) . join ( '' ) ; } // 4. Additional test cases it ( 'should ignore case and spaces' , ( ) => { expect ( isPalindrome ( 'A man a plan a canal Panama' ) ) . toBe ( true ) ; } ) ; it ( 'should return false for non-palindrome' , ( ) => { expect ( isPalindrome ( 'hello' ) ) . toBe ( false ) ; } ) ; Output format Testing strategy document

Testing Strategy

Coverage Goals

Unit Tests: 80%

Integration Tests: 60%

E2E Tests: Critical user flows

Test Execution

Unit: Every commit (local + CI)

Integration: Every PR

E2E: Before deployment

Tools

Unit: Jest

Integration: Supertest

E2E: Playwright

Coverage: Istanbul/nyc

CI/CD Integration

GitHub Actions: Run all tests on PR

Fail build if coverage < 80%

E2E tests on staging environment

Constraints

Required rules (MUST)

Test isolation

each test is independent

Fast feedback

unit tests should be fast (<1 min)

Deterministic

same input → same result

Prohibited items (MUST NOT)

Test dependencies

do not let test A depend on test B

Production DB

do not use a real DB in tests

Sleep/Timeout

avoid time-based tests

Best practices

AAA pattern

Arrange-Act-Assert

Test names

"should ... when ..."

Edge Cases

boundary values, null, empty values

Happy Path + Sad Path

both success/failure scenarios

References

Test Pyramid

Jest

Playwright

Testing Best Practices

Metadata

Version

Current version

1.0.0

Last updated

2025-01-01

Compatible platforms

Claude, ChatGPT, Gemini