analyzing-test-coverage

name	analyzing-test-coverage
description	Creates and analyzes tests using Vitest and MSW patterns. Generates test builders, mocks repositories, and configures integration tests. Triggers on: write tests, test coverage, Vitest, MSW mock, vi.fn, vi.mock, unit test, integration test, test builder, mock setup, test failure.
allowed-tools	Read, Grep, Glob, Write, Edit, Bash(pnpm test:*)

Testing Strategy Analyst

Purpose

Guide the creation of comprehensive tests following project patterns for unit tests, integration tests, and E2E tests using Vitest, MSW, and project-specific test helpers.

When to Use

• Writing new tests
• Analyzing test coverage gaps
• Setting up mocks for testing
• Organizing test files
• Debugging test failures

Table of Contents

• Testing Stack
• Test Organization
• Quick Pattern Reference
• Running Tests
• Test Quality Checklist
• Common Pitfalls
• References

Testing Stack

Tool	Purpose
Vitest	Test runner and assertion library
MSW	Mock Service Worker for network mocking
vi	Vitest mock utilities
test-helpers/	Project-specific test utilities

Test Organization

src/
├── modules/
│   └── category/
│       ├── category-service.ts
│       ├── category-service.test.ts        # Unit tests
│       ├── repository.ts
│       ├── repository.test.ts              # Repository tests
│       └── category.integration.test.ts    # Integration tests
├── core/
│   └── diff/
│       └── comparators/
│           ├── category-comparator.ts
│           └── category-comparator.test.ts
├── test-helpers/
│   ├── config-file-builder.ts
│   ├── graphql-mocks.ts
│   ├── config-fixtures.ts
│   └── cli-runner.ts
└── lib/
    └── test-setup.ts                       # Global test setup

e2e/
└── ...                                     # End-to-end tests

Quick Pattern Reference

Service Tests

See references/patterns.md for full examples. Key structure:

• Declare dependencies at suite level
• Reset mocks in beforeEach with vi.clearAllMocks()
• Use describe blocks for method grouping
• Follow Arrange-Act-Assert pattern

Repository Tests with MSW

See references/patterns.md for MSW setup. Key steps:

1. Define handlers with graphql.query() / graphql.mutation()
2. Setup server with beforeAll / afterAll
3. Override handlers for specific test cases with server.use()

Test Data Builders

See references/test-builders.md for implementations. Pattern:

• Create builder class with fluent interface
• Validate with Zod schema in build()
• Provide factory functions for convenience

Mock Functions

See references/patterns.md for examples. Common patterns:

• vi.fn() for simple mocks
• vi.mocked() for typed access
• vi.mock() for module mocking

Running Tests

# Run all tests
pnpm test

# Run specific test file
pnpm test -- --filter=category-service

# Run tests matching pattern
pnpm test -- --grep="should create category"

# Watch mode
pnpm test -- --watch

# With coverage
pnpm test -- --coverage

See references/commands-reference.md for advanced options and coverage configuration.

Test Quality Checklist

For Every Test

• Follows Arrange-Act-Assert pattern
• Has descriptive test name
• Tests one thing per test
• Includes both positive and negative cases
• Uses typed mocks (not any)
• Cleans up after itself (beforeEach/afterEach)

For Test Suites

• Covers all public methods
• Covers error scenarios
• Covers edge cases
• Uses schema-validated test data
• Has integration tests for complex flows

Validation Checkpoints

Phase	Validate	Command
Test written	File exists	Check *.test.ts created
Tests pass	All green	pnpm test <file>
Coverage adequate	Key paths covered	pnpm test --coverage
Mocks typed	No any in mocks	npx tsc --noEmit

Common Pitfalls

Not Resetting Mocks:

beforeEach(() => {
  vi.clearAllMocks(); // Always reset!
});

Testing Implementation Details:

// BAD - tests internal structure
expect(service.internalMap.size).toBe(1);

// GOOD - tests behavior
expect(await service.findBySlug('test')).toBeDefined();

Flaky Async Tests:

// BAD - race condition
const result = service.process();
expect(result).toBe(expected);

// GOOD - await properly
const result = await service.process();
expect(result).toBe(expected);

References

Skill Reference Files

• references/patterns.md - Detailed test patterns with full code examples
• references/test-builders.md - Builder pattern implementations
• references/commands-reference.md - Complete command reference

Project Resources

• {baseDir}/src/test-helpers/ - Test utilities
• {baseDir}/vitest.config.ts - Test configuration
• {baseDir}/docs/TESTING_PROTOCOLS.md - Testing protocols

External Documentation

• Vitest docs: https://vitest.dev
• MSW docs: https://mswjs.io

Related Skills

• Complete entity workflow: See adding-entity-types for E2E implementation including tests
• Zod test patterns: See designing-zod-schemas for schema validation tests
• GraphQL mocking: See writing-graphql-operations for MSW handlers

Quick Reference Rule

For a condensed quick reference, see .claude/rules/testing-standards.md (automatically loaded when editing *.test.ts files).