Teaches the agent to migrate a Jest suite to Vitest — vi.mock and the globals shim, vitest.config workspaces/projects, coverage, browser mode, and Vitest v4 breaking changes.
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Teaches the agent to migrate a Jest suite to Vitest — vi.mock and the globals shim, vitest.config workspaces/projects, coverage, browser mode, and Vitest v4 breaking changes.
This skill makes the agent migrate a Jest test suite to Vitest correctly and configure Vitest from scratch. Vitest is mostly Jest-compatible, but the differences bite: the vi namespace replaces jest, vi.mock hoisting needs vi.hoisted, ESM is first-class, and Vitest v4 removed workspace files in favor of inline projects. The agent should produce a config that runs fast, types cleanly, and reports coverage.
Use this skill when migrating from Jest, setting up vitest.config.ts, splitting unit vs browser tests, or resolving v4 upgrade breakage.
Core Principles
vi replaces jest.jest.fn -> vi.fn, jest.mock -> vi.mock, jest.spyOn -> vi.spyOn, jest.useFakeTimers -> vi.useFakeTimers. The assertion API (expect, matchers) is unchanged.
Mocks must reset explicitly. Set test.clearMocks/restoreMocks in config or call vi.clearAllMocks() in beforeEach — Vitest does not reset by default.
vi.mock is hoisted; use vi.hoisted for shared values. Variables the factory needs must be created via vi.hoisted(() => ...), since the factory runs before imports.
Decide on globals up front. Either enable globals: true (Jest-like, no imports) or import { describe, it, expect, vi } from vitest. Pick one and add types: ['vitest/globals'] if using globals.
v4 uses projects, not workspace. The standalone vitest.workspace.ts file is removed; declare multiple environments via the inline projects array.
Browser mode replaces jsdom for real-DOM tests. Use browser.instances (v4) to run component tests in a real browser engine via Playwright.
Workflow / Patterns
Pattern 1 — Mechanical Jest -> Vitest swap
Most test bodies migrate with a namespace rename. With , even the imports can stay as-is.
