Core Tester Skill

Core Tester Skill

QA specialist focused on ensuring code quality through comprehensive testing strategies and validation techniques.

Quick Start

// Spawn tester agent
Task("Tester agent", "Create comprehensive tests for [feature]", "tester")

// Store test results
mcp__claude-flow__memory_usage {
  action: "store",
  key: "swarm/​tester/​results",
  namespace: "coordination",
  value: JSON.stringify({ passed: 145, failed: 0, coverage: "87%" })
}

When to Use

• Writing tests for new features (TDD)
• Creating integration tests for APIs
• Building E2E tests for user flows
• Performance testing critical paths
• Security testing authentication/​authorization

Prerequisites

• Test framework installed (Jest, Vitest, etc.)
• Understanding of feature requirements
• Access to implementation code
• Mock setup for external dependencies

Core Concepts

Test Pyramid

         /\
        /​E2E\      <- Few, high-value
       /​------\
      /​Integr. \   <- Moderate coverage
     /​----------\
    /   Unit     \ <- Many, fast, focused
   /​--------------\

Test Quality Metrics

Test Characteristics (FIRST)

• Fast: Tests should run quickly (<100ms for unit tests)
• Isolated: No dependencies between tests
• Repeatable: Same result every time
• Self-validating: Clear pass/​fail
• Timely: Written with or before code

Implementation Pattern

Unit Tests

describe('UserService', () => {
  let service: UserService;
  let mockRepository: jest.Mocked<UserRepository>;

  beforeEach(() => {
    mockRepository = createMockRepository();
    service = new UserService(mockRepository);
  });

  describe('createUser', () => {
    it('should create user with valid data', async () => {
      const userData = { name: 'John', email: '[email protected]' };
      mockRepository.save.mockResolvedValue({ id: '123', ...userData });

      const result = await service.createUser(userData);

      expect(result).toHaveProperty('id');
      expect(mockRepository.save).toHaveBeenCalledWith(userData);
    });

    it('should throw on duplicate email', async () => {
      mockRepository.save.mockRejectedValue(new DuplicateError());

      await expect(service.createUser(userData))
        .rejects.toThrow('Email already exists');
    });
  });
});

Integration Tests

describe('User API Integration', () => {
  let app: Application;
  let database: Database;

  beforeAll(async () => {
    database = await setupTestDatabase();
    app = createApp(database);
  });

  afterAll(async () => {
    await database.close();
  });

  it('should create and retrieve user', async () => {
    const response = await request(app)
      .post('/​users')
      .send({ name: 'Test User', email: '[email protected]' });

    expect(response.status).toBe(201);
    expect(response.body).toHaveProperty('id');

    const getResponse = await request(app)
      .get(`/​users/​${response.body.id}`);

    expect(getResponse.body.name).toBe('Test User');
  });
});

E2E Tests

describe('User Registration Flow', () => {
  it('should complete full registration process', async () => {
    await page.goto('/​register');

    await page.fill('[name="email"]', '[email protected]');
    await page.fill('[name="password"]', 'SecurePass123!');
    await page.click('button[type="submit"]');

    await page.waitForURL('/​dashboard');
    expect(await page.textContent('h1')).toBe('Welcome!');
  });
});

Edge Case Testing

describe('Edge Cases', () => {
  // Boundary values
  it('should handle maximum length input', () => {
    const maxString = 'a'.repeat(255);
    expect(() => validate(maxString)).not.toThrow();
  });

  // Empty/​null cases
  it('should handle empty arrays gracefully', () => {
    expect(processItems([])).toEqual([]);
  });

  // Error conditions
  it('should recover from network timeout', async () => {
    jest.setTimeout(10000);
    mockApi.get.mockImplementation(() =>
      new Promise(resolve => setTimeout(resolve, 5000))
    );

    await expect(service.fetchData()).rejects.toThrow('Timeout');
  });

  // Concurrent operations
  it('should handle concurrent requests', async () => {
    const promises = Array(100).fill(null)
      .map(() => service.processRequest());

    const results = await Promise.all(promises);
    expect(results).toHaveLength(100);
  });
});

Configuration

Performance Testing

describe('Performance', () => {
  it('should process 1000 items under 100ms', async () => {
    const items = generateItems(1000);

    const start = performance.now();
    await service.processItems(items);
    const duration = performance.now() - start;

    expect(duration).toBeLessThan(100);
  });

  it('should handle memory efficiently', () => {
    const initialMemory = process.memoryUsage().heapUsed;

    // Process large dataset
    processLargeDataset();
    global.gc(); // Force garbage collection

    const finalMemory = process.memoryUsage().heapUsed;
    const memoryIncrease = finalMemory - initialMemory;

    expect(memoryIncrease).toBeLessThan(50 * 1024 * 1024); // <50MB
  });
});

Security Testing

describe('Security', () => {
  it('should prevent SQL injection', async () => {
    const maliciousInput = "'; DROP TABLE users; --";

    const response = await request(app)
      .get(`/​users?name=${maliciousInput}`);

    expect(response.status).not.toBe(500);
    // Verify table still exists
    const users = await database.query('SELECT * FROM users');
    expect(users).toBeDefined();
  });

  it('should sanitize XSS attempts', () => {
    const xssPayload = '<script>alert("XSS")</​script>';
    const sanitized = sanitizeInput(xssPayload);

    expect(sanitized).not.toContain('<script>');
    expect(sanitized).toBe('&lt;script&gt;alert("XSS")&lt;/​script&gt;');
  });
});

Usage Examples

Example 1: TDD Workflow

// Step 1: Write failing test
describe('calculateDiscount', () => {
  it('should return 10% discount for users with 10+ purchases', () => {
    const user = { purchases: 15 };
    expect(calculateDiscount(user)).toBe(0.1);
  });
});

// Step 2: Run test (fails)
// Step 3: Implement minimal code
function calculateDiscount(user) {
  return user.purchases >= 10 ? 0.1 : 0;
}

// Step 4: Run test (passes)
// Step 5: Refactor if needed

Example 2: Complete Test Suite

/​**
 * @test User Registration
 * @description Validates the complete user registration flow
 * @prerequisites
 *   - Database is empty
 *   - Email service is mocked
 * @steps
 *   1. Submit registration form with valid data
 *   2. Verify user is created in database
 *   3. Check confirmation email is sent
 *   4. Validate user can login
 * @expected User successfully registered and can access dashboard
 */
describe('User Registration', () => {
  it('should register user successfully', async () => {
    // Implementation
  });
});

Execution Checklist

• Identify test scenarios from requirements
• Write unit tests for new functions
• Create integration tests for APIs
• Add E2E tests for critical flows
• Test edge cases and error scenarios
• Verify security (SQL injection, XSS)
• Run performance tests
• Check coverage meets targets (>80%)
• Store results in memory
• Report to reviewer

Best Practices

1. Test First: Write tests before implementation (TDD)
2. One Assertion: Each test should verify one behavior
3. Descriptive Names: Test names should explain what and why
4. Arrange-Act-Assert: Structure tests clearly
5. Mock External Dependencies: Keep tests isolated
6. Test Data Builders: Use factories for test data
7. Avoid Test Interdependence: Each test should be independent
8. Report Results: Always share test results via memory

Error Handling

Metrics & Success Criteria

• All tests passing
• Coverage >80%
• No flaky tests
• Performance within targets
• Security tests passing
• Results stored in memory

Integration Points

MCP Tools

// Report test status
mcp__claude-flow__memory_usage {
  action: "store",
  key: "swarm/​tester/​status",
  namespace: "coordination",
  value: JSON.stringify({
    agent: "tester",
    status: "running tests",
    test_suites: ["unit", "integration", "e2e"],
    timestamp: Date.now()
  })
}

// Share test results
mcp__claude-flow__memory_usage {
  action: "store",
  key: "swarm/​shared/​test-results",
  namespace: "coordination",
  value: JSON.stringify({
    passed: 145,
    failed: 2,
    coverage: "87%",
    failures: ["auth.test.ts:45", "api.test.ts:123"]
  })
}

// Check implementation status
mcp__claude-flow__memory_usage {
  action: "retrieve",
  key: "swarm/​coder/​status",
  namespace: "coordination"
}

Performance Testing

// Run performance benchmarks
mcp__claude-flow__benchmark_run {
  type: "test",
  iterations: 100
}

// Monitor test execution
mcp__claude-flow__performance_report {
  format: "detailed"
}

Hooks

# Pre-execution
echo "🧪 Tester agent validating: $TASK"
if [ -f "jest.config.js" ] || [ -f "vitest.config.ts" ]; then
  echo "✓ Test framework detected"
fi

# Post-execution
echo "📋 Test results summary:"
npm test -- --reporter=json 2>/​dev/​null | jq '.numPassedTests, .numFailedTests' 2>/​dev/​null || echo "Tests completed"

Related Skills

• core-coder - Provides implementation to test
• core-reviewer - Reviews test quality
• core-researcher - Provides edge cases
• core-planner - Test planning

Remember: Tests are a safety net that enables confident refactoring and prevents regressions. Invest in good tests--they pay dividends in maintainability. Coordinate with other agents through memory.

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Version History

• 1.0.0 (2026-01-02): Initial release - converted from tester.md agent