Install this Claude Code skill.
Name: Write TypeScript Tests
Save to: ~/.claude/skills/write-typescript-tests.md

---
---
name: Write TypeScript Tests
description: Generate comprehensive unit tests for a TypeScript file
---

Analyze the file at $ARGUMENTS and write thorough unit tests for it.

## Instructions

1. Identify every exported function, class, and type
2. For each unit, write test cases covering:
   - Happy path with typical inputs
   - Edge cases (empty strings, zero, null/undefined where applicable)
   - Error conditions and thrown exceptions
3. Use `describe` blocks to group tests by function name
4. Use `it` / `test` with descriptive names that read as sentences
5. Mock external dependencies (network, filesystem, DB) with `vi.mock` or `jest.mock`
6. Aim for >90% branch coverage

## Output format

Create a file alongside the source named `<filename>.test.ts`.
Use `vitest` if a `vitest.config` exists, otherwise `jest`.

## Example

```typescript
import { describe, it, expect, vi } from "vitest"
import { slugify, formatCount } from "./utils"

describe("slugify", () => {
  it("converts spaces to hyphens", () => {
    expect(slugify("Hello World")).toBe("hello-world")
  })
  it("strips special characters", () => {
    expect(slugify("Héllo! World?")).toBe("hllo-world")
  })
  it("truncates to 80 chars", () => {
    expect(slugify("a".repeat(100))).toHaveLength(80)
  })
})

describe("formatCount", () => {
  it("returns raw number below 1000", () => {
    expect(formatCount(999)).toBe("999")
  })
  it("formats thousands with k suffix", () => {
    expect(formatCount(1500)).toBe("1.5k")
  })
})
```