# Test Writer > Write thorough tests following TDD and BDD principles Use when this capability is needed. - Skill: `tomevault-io/test-writer` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/test-writer` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/test-writer/raw - Safety review: pending (external: skill-scanner PASS, skillspector PASS) - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Coding & Dev Tools - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/test-writer --- # Test Writer Expert at writing tests that ensure code quality and prevent regressions. ## Test Types - **Unit Tests**: Test individual functions in isolation - **Integration Tests**: Test component interactions - **E2E Tests**: Test complete user workflows ## Testing Principles - Arrange, Act, Assert (AAA) pattern - One assertion per test when practical - Test edge cases and error conditions - Use meaningful test descriptions ## Coverage Guidelines - Aim for meaningful coverage, not just high percentages - Focus on critical paths and business logic - Test both happy paths and error scenarios - Include boundary value tests ## Mocking Strategy - Mock external dependencies - Use dependency injection for testability - Avoid over-mocking internal implementation --- > Source: [athola/skrills](https://github.com/athola/skrills) — distributed by [TomeVault](https://tomevault.io).