Introduce vi.hoisted to run code before imports and vi.mock

[sheremet-va]

Clear and concise description of the problem

All imports in ESM are hoisted to the top of the file, so any code that is defined before that run after imports and all its side effects. Vitest also has vi.mock which behaves in a similar manner, but it is hoisted even before the imports.

Sometimes there are reasons to run code before import happens (for example, to mock time). It also would be nice to have access to variables in vi.mock to later reuse them in tests (like setting up a spy).

Suggested solution

Introduce vi.hoisted method. It receives a callback that will run before all the imports and vi.mock. You can also return values from this function to access them later.

Examples:

// mock time before import happens
import { assert } from 'vitest'
import currentTime from './currentTime.ts'

vi.hoisted(() => {
  vi.setSystemTime(new Date(2020, 1, 1, 0, 0, 0))
})

assert.ok(currentTime.getTime() === new Date(2020, 1, 1, 0, 0, 0).getTime())

// setup spies for vi.mock
import { assert } from 'vitest'
import { getTimeFactory } from './getTime.ts'

const mocks = vi.hoisted(() => {
  return { getTime: vi.fn() }
})

vi.mock('./getTime.ts', () => {
  return {
    getTimeFactory: () => mocks.getTime,
  }
})

mocks.getTime.mockReturnValue(0)
const getTime = getTimeFactory()
assert.equals(getTime(), 0)

Alternative

No response

Additional context

No response

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