vi.mock is hoisted to the top of the file. That single fact explains almost every "my mock isn't working" bug in Vitest.
You wrote a mock. The test still hits the real module. Nothing in the error message points at why.
import { fetchUser } from './api'
import { vi, test, expect } from 'vitest'
const mockFetch = vi.fn()
vi.mock('./api', () => ({ fetchUser: mockFetch })) // ReferenceError
The API is compatible enough that the migration looks free. These five differences are where the afternoon actually goes.
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