Test Strategy Design

Systematic patterns for designing comprehensive test strategies that balance coverage, speed, and maintainability.

When to Activate

• Designing test strategy for new projects
• Improving existing test coverage
• Setting up test automation frameworks
• Configuring CI/CD quality gates
• Analyzing test gaps and priorities
• Establishing testing standards for teams

The Test Pyramid

The test pyramid guides the distribution of testing effort:

                 ┌─────────┐
                 │   E2E   │  ~10% - Critical user journeys
                 │ Tests   │  Slow, expensive, high confidence
                 ├─────────┤
                 │ Integr- │  ~20% - Component interactions
                 │  ation  │  Medium speed, real dependencies
                 ├─────────┤
                 │  Unit   │  ~70% - Business logic
                 │  Tests  │  Fast, isolated, cheap
                 └─────────┘

Layer Characteristics

Layer	Speed	Isolation	Confidence	Maintenance
Unit	< 10ms	Complete	Low per test	Low
Integration	< 1s	Partial	Medium	Medium
E2E	< 30s	None	High	High

When to Test at Each Layer

Unit Tests - Test here when:

• Pure business logic
• Algorithmic code
• Data transformations
• Validation rules
• Edge cases and boundaries

Integration Tests - Test here when:

• Database interactions
• API contracts
• Service communication
• File system operations
• Cache behavior

E2E Tests - Test here when:

• Critical user journeys
• Cross-system workflows
• Authentication flows
• Payment processes
• Smoke tests for deployments

Test Design Patterns

Unit Test Patterns

Arrange-Act-Assert (AAA)

// Arrange: Set up test data and dependencies
const user = createUser({ email: 'test@example.com' });
const validator = new EmailValidator();

// Act: Execute the behavior under test
const result = validator.validate(user.email);

// Assert: Verify the expected outcome
expect(result.isValid).toBe(true);

One Assertion Per Test

Focus each test on a single behavior:

// Bad: Multiple unrelated assertions
test('user validation', () => {
  expect(user.isValid()).toBe(true);
  expect(user.email).toContain('@');
  expect(user.createdAt).toBeDefined();
});

// Good: Separate tests for each behavior
test('validates user with proper email', () => {
  expect(user.isValid()).toBe(true);
});

test('email contains @ symbol', () => {
  expect(user.email).toContain('@');
});

Descriptive Test Names

Test names should describe the expected behavior:

// Bad
test('email test', () => { ... });

// Good
test('rejects email without domain', () => { ... });
test('accepts email with subdomain', () => { ... });
test('trims whitespace from email input', () => { ... });

Test Data Builders

Create readable test data:

// Builder pattern for test data
const user = UserBuilder.create()
  .withEmail('test@example.com')
  .withRole('admin')
  .withActiveSubscription()
  .build();

Integration Test Patterns

Test Through Public Interfaces

// Bad: Testing internal implementation
test('repository uses correct SQL', () => {
  const sql = userRepo.buildQuery();
  expect(sql).toContain('SELECT * FROM users');
});

// Good: Testing behavior through public API
test('finds users by email domain', async () => {
  await userRepo.save(createUser({ email: 'a@corp.com' }));
  await userRepo.save(createUser({ email: 'b@corp.com' }));

  const users = await userRepo.findByDomain('corp.com');

  expect(users).toHaveLength(2);
});

Use Real Dependencies Where Practical

// Prefer real database for repository tests
beforeAll(async () => {
  testDb = await createTestDatabase();
});

afterEach(async () => {
  await testDb.truncateAll();
});

// Mock only external services
jest.mock('./paymentGateway', () => ({
  charge: jest.fn().mockResolvedValue({ success: true })
}));

Contract Testing

Verify API contracts between services:

// Consumer contract
describe('User API Contract', () => {
  test('GET /users/:id returns user shape', async () => {
    const response = await api.get('/users/123');

    expect(response).toMatchSchema({
      id: expect.any(String),
      email: expect.any(String),
      createdAt: expect.any(String),
    });
  });
});

E2E Test Patterns

Critical Path Focus

Only test the most important user journeys:

// Priority 1: Revenue-critical paths
test('complete purchase flow', async () => {
  await page.addToCart(product);
  await page.checkout();
  await page.enterPayment(validCard);
  await page.confirmOrder();

  await expect(page.orderConfirmation).toBeVisible();
});

// Priority 2: Core functionality
test('user registration and login', async () => {
  await page.register(newUser);
  await page.login(newUser);

  await expect(page.dashboard).toBeVisible();
});

Page Object Pattern

Encapsulate page interactions:

class CheckoutPage {
  constructor(page) {
    this.page = page;
  }

  async enterShippingAddress(address) {
    await this.page.fill('#street', address.street);
    await this.page.fill('#city', address.city);
    await this.page.fill('#zip', address.zip);
  }

  async submitOrder() {
    await this.page.click('[data-testid="submit-order"]');
    await this.page.waitForURL('**/confirmation');
  }
}

Resilient Selectors

Use stable selectors that survive UI changes:

// Fragile: Based on CSS/position
await page.click('.btn-primary');
await page.click('div > div:nth-child(2) > button');

// Stable: Based on test IDs or roles
await page.click('[data-testid="submit-button"]');
await page.getByRole('button', { name: 'Submit' });

Coverage Strategy

Coverage Types

Type	Measures	Target
Line	Lines executed	80%
Branch	Decision paths taken	75%
Function	Functions called	90%
Statement	Statements executed	80%

Coverage Prioritization

Focus coverage on high-risk areas:

High Priority (100% coverage):
├── Payment processing
├── Authentication/Authorization
├── Data validation
├── Business rule enforcement
└── Security-sensitive code

Medium Priority (80% coverage):
├── Core business logic
├── API endpoints
├── Data transformations
└── Error handling

Lower Priority (60% coverage):
├── UI components
├── Configuration
├── Logging/Monitoring
└── Admin features

Meaningful Coverage

Coverage quantity vs quality:

// 100% coverage, low value
test('getter returns value', () => {
  user.name = 'John';
  expect(user.name).toBe('John');
});

// 80% coverage, high value
test('rejects order when inventory insufficient', () => {
  const inventory = createInventory({ quantity: 5 });
  const order = createOrder({ quantity: 10 });

  expect(() => processOrder(order, inventory))
    .toThrow('Insufficient inventory');
});

Quality Gates

Gate Configuration

Gate	Threshold	Enforcement
Unit Tests	100% pass	Block merge
Integration Tests	100% pass	Block merge
E2E Tests	100% pass	Block deploy
Line Coverage	≥ 80%	Block merge
Branch Coverage	≥ 75%	Block merge
New Code Coverage	≥ 90%	Warn
Test Duration	< 10 min	Warn

Flaky Test Management

Flaky Test Protocol:
1. DETECT: Track test stability over time
2. QUARANTINE: Move flaky tests to separate suite
3. FIX: Prioritize fixing within 1 week
4. REINTEGRATE: Return to main suite after 10 consecutive passes

Test Performance Budgets

Test Type	Target Duration	Action if Exceeded
Single Unit Test	< 10ms	Investigate
Unit Suite	< 30s	Parallelize
Single Integration	< 1s	Review setup/teardown
Integration Suite	< 2 min	Parallelize
Single E2E	< 30s	Optimize waits
E2E Suite	< 10 min	Reduce scope

Test Organization

File Structure

src/
├── user/
│   ├── User.ts
│   ├── User.test.ts           # Unit tests co-located
│   ├── UserRepository.ts
│   └── UserRepository.test.ts
├── order/
│   ├── Order.ts
│   └── Order.test.ts
tests/
├── integration/
│   ├── api/
│   │   └── users.test.ts      # API integration tests
│   └── database/
│       └── repositories.test.ts
└── e2e/
    ├── checkout.spec.ts       # E2E tests by journey
    └── registration.spec.ts

Test Naming Conventions

# Unit tests: [unit].test.ts
User.test.ts
OrderCalculator.test.ts

# Integration tests: [feature].integration.test.ts
users.integration.test.ts
payment-gateway.integration.test.ts

# E2E tests: [journey].e2e.ts or [journey].spec.ts
checkout.e2e.ts
user-onboarding.spec.ts

Test Data Management

Test Data Principles

1. Isolation: Each test manages its own data
2. Cleanup: Tests clean up after themselves
3. Determinism: Same test, same data, same result
4. Minimal: Only create data needed for the test

Factories and Fixtures

// Factory: Dynamic test data
const createUser = (overrides = {}) => ({
  id: faker.string.uuid(),
  email: faker.internet.email(),
  name: faker.person.fullName(),
  ...overrides
});

// Fixture: Static reference data
const ADMIN_USER = {
  id: 'admin-001',
  email: 'admin@test.com',
  role: 'admin'
};

Database Test Patterns

// Transaction rollback pattern
beforeEach(async () => {
  transaction = await db.beginTransaction();
});

afterEach(async () => {
  await transaction.rollback();
});

// Truncate pattern (slower but more isolated)
afterEach(async () => {
  await db.truncateAll();
});

CI/CD Integration

Pipeline Configuration

test:
  stages:
    - lint-and-typecheck    # Fast feedback first
    - unit-tests            # Parallel execution
    - integration-tests     # With test database
    - e2e-tests             # Against staging environment

  parallelization:
    unit: 4 workers
    integration: 2 workers
    e2e: 1 worker (sequential for stability)

  artifacts:
    - coverage reports
    - test results (JUnit XML)
    - E2E screenshots/videos on failure

Failure Handling

On Test Failure:
1. Capture: Screenshots, logs, database state
2. Report: Notify team channel
3. Block: Prevent merge/deploy
4. Retry: Once for E2E (flaky detection)

Best Practices

Do

• Test behavior, not implementation
• Keep tests independent and isolated
• Use meaningful, descriptive test names
• Maintain test code like production code
• Run tests frequently during development
• Fix flaky tests immediately

Avoid

• Testing private methods directly
• Mocking everything (use real dependencies where practical)
• Ignoring slow tests (fix the root cause)
• Writing tests after bugs (write them before)
• Sharing state between tests
• Over-relying on E2E tests

References

• Test Pattern Examples - Code examples for each pattern
• Framework-Specific Guides - Jest, Pytest, Go testing patterns