Testing Expert Skill Skill

Testing Expert Skill

Expert in testing strategies for React, Next.js, and NestJS applications.

When to Use This Skill

Writing unit tests
Creating integration tests
Setting up E2E tests
Testing React components
Testing API endpoints
Testing database operations
Setting up test infrastructure
Reviewing test coverage

Project Context Discovery

Scan Documentation: Check .agents/SYSTEM/ARCHITECTURE.md for testing architecture
Identify Tools: Jest/Vitest, React Testing Library, Supertest, Playwright/Cypress
Discover Patterns: Review existing test files, utilities, mocking patterns
Use Project-Specific Skills: Check for [project]-testing-expert skill

Core Testing Principles

Testing Pyramid

Unit Tests (70%): Fast, isolated, test individual functions/components
Integration Tests (20%): Test component interactions
E2E Tests (10%): Test full user flows

Coverage Targets

Line coverage: > 80%
Branch coverage: > 75%
Function coverage: > 85%
Critical paths: 100%

Test Organization

src/
  users/
    users.controller.ts
    users.controller.spec.ts  # Unit tests
    users.service.ts
    users.service.spec.ts
  __tests__/
    integration/
    e2e/

Test Quality (AAA Pattern)

it('should return users filtered by organization', async () => {
  // Arrange: Set up test data
  const organizationId = 'org1';
  const expectedUsers = [{ organization: organizationId }];

  // Act: Execute the code being tested
  const result = await service.findAll(organizationId);

  // Assert: Verify the result
  expect(result).toEqual(expectedUsers);
});

Good Tests Are

Independent (no test dependencies)
Fast (< 100ms each)
Repeatable (same result every time)
Meaningful (test real behavior)
Maintainable (easy to update)

Testing Best Practices Summary

Test Isolation: Each test independent, clean up after
Meaningful Tests: Test behavior, not implementation
Mocking Strategy: Mock external dependencies, not what you're testing
Test Data: Use factories, keep data minimal, clean up
Coverage: High coverage, focus on critical paths

Integration

| Test Type | Tools | Use Case | |-----------|-------|----------| | Unit | Jest/Vitest | Functions, components, services | | Integration | Supertest + Jest | Controller + Service + DB | | E2E | Playwright/Cypress | Full user flows | | Component | React Testing Library | React component behavior |

For complete React Testing Library examples, hook testing, Next.js page/API testing, NestJS service/controller testing, integration test setup, E2E test patterns, MongoDB testing, authentication helpers, test fixtures, and mocking patterns, see: references/full-guide.md

Agent Skills: Testing Expert Skill

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Skill Files