Test Generator

Purpose: Analyze source code and generate comprehensive unit tests following the project's testing conventions.

Invocation

/test-gen <file_path> [--framework vitest|jest|pytest|go]

Process

Step 1: Analyze the Target

Read the source file and identify:

• All exported functions/classes/methods
• Input types and return types
• Edge cases from conditional branches
• Dependencies that need mocking
• Existing test file (if any) to avoid duplicates

Step 2: Determine Testing Framework

Auto-detect from project config:

• vitest.config.* → Vitest
• jest.config.* or package.json[jest] → Jest
• pytest.ini or pyproject.toml[tool.pytest] → pytest
• *_test.go files → Go testing

Step 3: Generate Test Cases

For each function, generate:

1. Happy path — typical valid input → expected output
2. Edge cases — empty input, zero, null/undefined, boundary values
3. Error paths — invalid input → expected error/exception
4. Type variations — different valid types if function accepts union types

Step 4: Structure the Test File

import { describe, it, expect, vi } from 'vitest'
import { targetFunction } from '../path/to/source'

describe('targetFunction', () => {
  it('returns expected result for valid input', () => {
    expect(targetFunction('valid')).toBe('expected')
  })

  it('throws on null input', () => {
    expect(() => targetFunction(null)).toThrow()
  })

  it('handles empty string', () => {
    expect(targetFunction('')).toBe('')
  })
})

Mocking Strategy

• External APIs: Always mock with vi.mock() or jest.mock()
• Database calls: Mock the client/ORM, not the database
• File system: Mock fs operations, never touch real files
• Time: Use vi.useFakeTimers() for time-dependent logic
• Environment variables: Set via vi.stubEnv() or test setup

Rules

• Match the project's existing test style (describe/it vs test, assertion style)
• Place test files adjacent to source (*.test.ts) or in tests/ mirror
• Never generate snapshot tests unless explicitly asked
• Aim for branch coverage, not just line coverage
• Each test should be independent — no shared mutable state
• Test names should describe behavior, not implementation

Playground

<span style='color:#8b949e'>Language: TypeScript / Vitest</span>

<span style='color:#8b949e'>Parses a currency string like</span> <span style='color:#8b949e'>"$1,234.56" → 1234.56 (number).</span> <span style='color:#8b949e'>Throws if input is not a valid</span> <span style='color:#8b949e'>currency string.</span></pre></div><div class='panel'><div class='label'>Output: Test suite</div><pre><span style='color:#58a6ff'>describe('parseAmount', () => {</span> <span style='color:#3fb950'> it('parses USD with commas', () =></span> <span style='color:#8b949e'> expect(parseAmount('$1,234.56'))</span> <span style='color:#8b949e'> .toBe(1234.56))</span>

<span style='color:#3fb950'> it('parses zero', () =></span> <span style='color:#8b949e'> expect(parseAmount('$0.00')).toBe(0))</span>

<span style='color:#3fb950'> it('throws on empty string', () =></span> <span style='color:#8b949e'> expect(() => parseAmount(''))</span> <span style='color:#8b949e'> .toThrow())</span>

<span style='color:#3fb950'> it('throws on plain text', () =></span> <span style='color:#8b949e'> expect(() => parseAmount('hello'))</span> <span style='color:#8b949e'> .toThrow())</span> <span style='color:#58a6ff'>})</span></pre></div></div></body></html>