# Test Writer

> Write comprehensive tests following TDD principles Use when this capability is needed.

- Skill: `tomevault-io/test-writer-5` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/test-writer-5`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/test-writer-5/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-5

---


# Test Writer Skill

## When to Use

Use this skill when you need to:
- Write tests for new features
- Add tests for existing code (increase coverage)
- Write integration or E2E tests

## Instructions

### Step 1: Understand the Requirements

Read the acceptance criteria and identify:
- Happy path scenarios
- Edge cases
- Error conditions
- Integration points

### Step 2: Choose Test Type

| Scenario | Test Type | Framework |
|----------|-----------|-----------|
| Single function/class | Unit test | pytest / jest |
| Multiple components | Integration | pytest / jest |
| Full user flow | E2E | Playwright |
| API endpoints | API test | httpx / supertest |

### Step 3: Write Tests

#### Unit Test Template (Python)
```python
import pytest
from src.module import function_under_test

class TestFunctionName:
    """Tests for function_name."""

    def test_happy_path(self):
        """Test normal operation."""
        result = function_under_test(valid_input)
        assert result == expected_output

    def test_edge_case_empty_input(self):
        """Test with empty input."""
        result = function_under_test([])
        assert result == []

    def test_error_invalid_input(self):
        """Test error handling for invalid input."""
        with pytest.raises(ValueError, match="Invalid input"):
            function_under_test(invalid_input)
```

#### Unit Test Template (TypeScript)
```typescript
import { describe, it, expect } from 'vitest';
import { functionUnderTest } from '../src/module';

describe('functionName', () => {
  it('should handle normal operation', () => {
    const result = functionUnderTest(validInput);
    expect(result).toEqual(expectedOutput);
  });

  it('should handle edge case with empty input', () => {
    const result = functionUnderTest([]);
    expect(result).toEqual([]);
  });

  it('should throw error for invalid input', () => {
    expect(() => functionUnderTest(invalidInput)).toThrow('Invalid input');
  });
});
```

### Step 4: Run and Verify Failure

```bash
# Python
pytest tests/test_new_feature.py -v

# TypeScript
npm test -- tests/new-feature.test.ts
```

Tests MUST fail before implementation.

### Step 5: Report

```json
{
  "status": "tests_written",
  "tests_count": 5,
  "test_file": "tests/test_feature.py",
  "ready_for_implementation": true
}
```

---
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<!-- tomevault:4.0:skill_md:2026-04-16 -->