vitest-mocking

Installation
SKILL.md

Vitest Mocking

Test Double Types

Type Purpose Changes Implementation?
Spy Record calls, verify interactions No (uses real code)
Mock Replace module entirely Yes
Stub Return canned responses Yes
Fake Working but simplified impl Yes

Decision Guide

Use spy when: Verifying a function was called correctly while keeping real behavior

const fetchSpy = vi.spyOn(globalThis, "fetch");
await doSomething();
expect(fetchSpy).toHaveBeenCalledWith("https://api.example.com");
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Installs
15
GitHub Stars
12
First Seen
Jan 24, 2026