test-generator - SKILL.md Agent Skill

name: test-generator description: | Analyzes existing code and auto-generates unit and integration tests. Covers happy paths, edge cases, and error scenarios for Jest, Vitest, pytest, and Kotest frameworks. metadata: version: 1.0.0 category: development domain: testing triggers: - "generate tests" - "write tests" - "add tests" - "test coverage"

Test Generator - Automated Test Generation

Overview

Reads existing code and generates comprehensive test suites. Covers the boring-but-critical test writing so developers can focus on business logic.

1. When to Apply

Trigger	Behavior
"generate tests for [file]"	Analyze file, generate test suite
"add tests"	Scan for untested code, generate tests
"test coverage"	Identify coverage gaps, generate missing tests

2. Test Generation Workflow

Step 1: Code Analysis

1. Read target file(s)
2. Identify exported functions/classes/methods
3. Analyze parameter types and return types
4. Detect dependencies (imports, injections)
5. Identify side effects (API calls, DB, file system)

Step 2: Test Case Planning

For each function, generate test cases:

Category	Examples
Happy path	Valid inputs → expected output
Boundary values	0, 1, MAX, empty string, empty array
Invalid inputs	null, undefined, wrong type, negative
Error handling	Network failure, timeout, invalid response
Edge cases	Concurrent calls, unicode, special chars

Step 3: Test Generation

TypeScript (Jest/Vitest):

import { describe, it, expect, vi } from 'vitest'
import { calculatePrice } from './pricing'

describe('calculatePrice', () => {
  it('calculates base price correctly', () => {
    expect(calculatePrice({ quantity: 1, unitPrice: 100 })).toBe(100)
  })

  it('applies discount for bulk orders', () => {
    expect(calculatePrice({ quantity: 100, unitPrice: 10 })).toBe(900)
  })

  it('throws for negative quantity', () => {
    expect(() => calculatePrice({ quantity: -1, unitPrice: 10 }))
      .toThrow('Quantity must be positive')
  })

  it('returns 0 for zero quantity', () => {
    expect(calculatePrice({ quantity: 0, unitPrice: 100 })).toBe(0)
  })
})

Python (pytest):

import pytest
from pricing import calculate_price

def test_base_price():
    assert calculate_price(quantity=1, unit_price=100) == 100

def test_bulk_discount():
    assert calculate_price(quantity=100, unit_price=10) == 900

def test_negative_quantity_raises():
    with pytest.raises(ValueError, match="positive"):
        calculate_price(quantity=-1, unit_price=10)

def test_zero_quantity():
    assert calculate_price(quantity=0, unit_price=100) == 0

Step 4: Mock Generation

Auto-generate mocks for external dependencies:

// Auto-detected: function calls supabase
vi.mock('@/lib/supabase', () => ({
  supabase: {
    from: vi.fn(() => ({
      select: vi.fn().mockResolvedValue({ data: mockData, error: null })
    }))
  }
}))

3. Framework Detection

File Pattern	Framework
`vitest.config.*`	Vitest
`jest.config.*`	Jest
`pytest.ini`, `pyproject.toml` with pytest	pytest
`build.gradle*` with kotest	Kotest

4. Tool Coordination

Tool	Purpose
Read	Analyze source code
Write	Generate test files
Glob	Find test config, existing tests
Grep	Detect imports, dependencies
Bash	Run tests, check coverage

5. Boundaries

Will:

Generate test suites for functions/classes/endpoints
Cover happy paths, edge cases, and error scenarios
Auto-generate mocks for external dependencies
Follow existing test conventions in the project

Will Not:

Write E2E tests (use e2e-runner agent)
Replace TDD workflow (use tdd-guide agent for that)
Guarantee 100% coverage (focuses on meaningful tests)
Test private/internal implementation details