testing

Testing Software

MCP Tools

Chrome DevTools (E2E testing):

• Automate user flows in real browser
• Capture screenshots for visual regression
• Run Lighthouse for accessibility testing
• Profile performance during test runs

Testing Pyramid

1. Unit Tests (Many): Fast, isolated, test single units
2. Integration Tests (Some): Test component interactions
3. E2E Tests (Few): Test complete user flows — use Chrome DevTools

Workflows

• Analyze: Use Glob and Grep to identify untested code
• Unit Tests: Cover all public functions
• Edge Cases: Test boundaries and error conditions
• Integration: Test external dependencies
• E2E: Use Chrome DevTools for browser automation
• Regression: Add test for each bug fix

Test-Driven Development

When writing new logic, default to red-green-refactor:

1. Red: Write a failing test for one behavior before writing the implementation.
2. Green: Write the minimum code needed to make that test pass.
3. Refactor: Clean up structure only while the suite is green — no new behavior in this step.

• One behavior per test — if a test needs "and" to describe it, split it.
• Never write production code without a failing test driving it, except for spikes/throwaway exploration (delete or backfill tests before merging).
• Don't refactor and add behavior in the same commit; commit on green before switching hats (see code-quality.md Two Hats Rule).

When TDD is the right default: new business logic, bug fixes (write the regression test first, watch it fail, then fix), and any code with clear input/output contracts.

When it isn't: exploratory spikes, throwaway scripts, UI layout/styling tweaks, and generated boilerplate — write tests after the shape stabilizes instead.

Test Quality Standards

Deterministic

Tests must produce the same result every time.

Isolated

Tests should not depend on each other or shared state.

Clear

Test names should describe the behavior being tested.

Test Patterns

Arrange-Act-Assert (AAA) (TypeScript Example)

test("user registration sends welcome email", async () => {
  // Arrange
  const emailService = new MockEmailService();
  const userService = new UserService(emailService);

  // Act
  await userService.register("[email protected]");

  // Assert
  expect(emailService.sentEmails).toContainEqual({
    to: "[email protected]",
    subject: "Welcome!"
  });
});

E2E Testing with Chrome DevTools

// Use Chrome DevTools MCP for browser automation
// - Navigate to pages
// - Fill forms and click buttons
// - Capture screenshots for visual regression
// - Run Lighthouse accessibility audits
// - Check console for errors

Commands (Examples by Language)

# Run tests
npm test
pytest
go test ./...

# With coverage
npm test -- --coverage
pytest --cov=src
go test -cover ./...

Finding Untested Code

Use Glob and Grep to identify gaps:

1. Use Glob to find all source files and test files
2. Check which source files have corresponding test files
3. Use Grep to see if functions are referenced in tests