Agent skill

test-specialist

This skill should be used when writing test cases, fixing bugs, analyzing code for potential issues, or improving test coverage for JavaScript/TypeScript applications. Use this for unit tests, integration tests, end-to-end tests, debugging runtime errors, logic bugs, performance issues, security vulnerabilities, and systematic code analysis.

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npx add-skill https://github.com/majiayu000/claude-skill-registry/tree/main/skills/other/test-specialist

SKILL.md

Test Specialist

Systematic testing methodologies and debugging techniques for JS/TS applications.

When to Use

Use for:

  • Writing unit, integration, or E2E tests
  • Fixing bugs and debugging
  • Improving test coverage
  • Analyzing code for potential issues
  • Security and performance testing

Don't use when:

  • Code review → use generic-code-reviewer
  • Technical debt → use tech-debt-analyzer
  • Feature development → use generic-feature-developer

Testing Stack by Project

Project Type Unit Tests Component E2E
React/Next.js Vitest/Jest Testing Library Playwright
Node.js Vitest/Jest Supertest Playwright
Static Jest - Playwright

Test Patterns

Unit Tests (AAA Pattern)

typescript
describe("calculateTotal", () => {
  test("sums amounts correctly", () => {
    // Arrange
    const items = [{ amount: 100 }, { amount: 50 }];
    // Act
    const total = calculateTotal(items);
    // Assert
    expect(total).toBe(150);
  });

  test("handles empty list", () => {
    expect(calculateTotal([])).toBe(0);
  });
});

Component Tests (User Behavior)

typescript
// ✅ Test user behavior, not implementation
it('creates item when user clicks Add', async () => {
  const user = userEvent.setup();
  render(<ItemList />);

  await user.click(screen.getByRole('button', { name: /add/i }));
  await user.type(screen.getByLabelText(/title/i), 'New item');
  await user.click(screen.getByRole('button', { name: /save/i }));

  expect(screen.getByText('New item')).toBeInTheDocument();
});

E2E Tests (Playwright)

typescript
import { test, expect } from "@playwright/test";

test("user can complete checkout", async ({ page }) => {
  await page.goto("/products");

  // Add to cart
  await page.click('button:has-text("Add to Cart")');
  await page.click('a:has-text("Cart")');

  // Checkout
  await page.click('button:has-text("Checkout")');
  await page.fill('[name="email"]', "[email protected]");
  await page.click('button:has-text("Place Order")');

  // Verify
  await expect(page.locator("h1")).toContainText("Order Confirmed");
});

Integration Tests

typescript
test("POST /items creates item", async () => {
  const response = await request(app)
    .post("/api/items")
    .send({ name: "Test" })
    .expect(201);

  expect(response.body).toMatchObject({ id: expect.any(Number) });
});

Bug Analysis Process

  1. Reproduce - Document exact steps, expected vs actual
  2. Isolate - Binary search, minimal reproduction
  3. Root Cause - Trace execution, check assumptions, git blame
  4. Fix - Write failing test first, implement fix
  5. Validate - Run full suite, test edge cases

Debugging Checklist

When debugging an issue:

  • Can reproduce consistently
  • Minimal reproduction created
  • Console/network logs checked
  • State at failure point inspected
  • Git blame checked for recent changes
  • Failing test written before fix

Common Bug Patterns

Race Conditions

typescript
test("handles concurrent updates", async () => {
  const promises = Array.from({ length: 100 }, () => increment());
  await Promise.all(promises);
  expect(getCount()).toBe(100);
});

Null Safety

typescript
test.each([null, undefined, "", 0])("handles invalid input: %p", (input) => {
  expect(() => process(input)).toThrow("Invalid");
});

Boundary Values

typescript
test("handles edge cases", () => {
  expect(paginate([], 1, 10)).toEqual([]); // empty
  expect(paginate([item], 1, 10)).toEqual([item]); // single
  expect(paginate(items25, 3, 10)).toHaveLength(5); // partial last page
});

Security Tests

typescript
test("prevents SQL injection", async () => {
  const malicious = "'; DROP TABLE users; --";
  await expect(search(malicious)).resolves.not.toThrow();
});

test("sanitizes XSS", () => {
  const xss = '<script>alert("xss")</script>';
  expect(sanitize(xss)).not.toContain("<script>");
});

test("requires auth", async () => {
  await request(app).post("/api/items").expect(401);
});

Performance Tests

typescript
test("handles large datasets efficiently", () => {
  const largeList = Array.from({ length: 10000 }, (_, i) => ({ value: i }));
  const start = performance.now();
  process(largeList);
  expect(performance.now() - start).toBeLessThan(100);
});

Coverage Targets

Code Type Target
Critical paths 90%+
Business logic 85%+
UI components 75%+
Utilities 70%+

Test Quality Principles

  1. One behavior per test
  2. Descriptive names - test names explain scenario
  3. Independent tests - no shared state
  4. Cover edge cases - null, empty, boundaries, errors
  5. Mock external deps - tests should be fast
  6. Test behavior - not implementation details

Workflow Decision Tree

Situation Action
Adding feature Write test first (TDD)
Fixing bug Write failing test, then fix
Improving coverage Find gaps, prioritize critical paths
Code review Check edge cases, error handling

See Also

  • Code Review Standards - Quality requirements
  • Project CLAUDE.md - Testing rules

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