# Analyzing Test Coverage

> Creates and analyzes tests using Vitest and MSW patterns. Use when writing unit tests, integration tests, analyzing coverage gaps, setting up MSW handlers, vi.fn mocks, test builders, or debugging test failures. Do NOT use for non-test TypeScript code.

- Skill: `tomevault-io/analyzing-test-coverage` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/analyzing-test-coverage`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/analyzing-test-coverage/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Integrations & APIs
- Author: tomevault-io (https://skillmd.com/u/tomevault-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tomevault-io/analyzing-test-coverage

---


# Testing Strategy Analyst

## Overview

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 for entities or services
- Analyzing test coverage gaps
- Setting up mocks (MSW handlers, vi.fn)
- Organizing test files in the module structure
- Debugging test failures

## 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

```bash
pnpm test                                    # All tests
pnpm test -- --filter=category-service       # Specific file
pnpm test -- --grep="should create category" # Pattern match
pnpm test -- --watch                         # Watch mode
pnpm test -- --coverage                      # With 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 Mistakes

| Mistake | Fix |
|---------|-----|
| Not resetting mocks | Add `vi.clearAllMocks()` in `beforeEach` |
| Testing implementation details | Test behavior (public API output), not internal state |
| Flaky async tests | Always `await` async operations before asserting |
| Using `any` in mocks | Use `vi.mocked()` for typed mock access |
| Missing error case tests | Add tests for rejection, validation failure, empty input |

## 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).

---
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<!-- tomevault:4.0:skill_md:2026-04-11 -->