Import order breaks tests when using vi.mock

[gabz75]

Describe the bug

The stackblitz below illustrates the issue.

Let's say I have a function main that calls a function foobar. When testing main, I would like to mock foobar and have the mock implementation in a separate file.

In my test file, if I import the file with the mock implementation BEFORE the file where the function main is, everything works fine.

However if I import the file with the mock implementation AFTER the file where the function main is,vitest complains with the following hoisting error:

Notes: this example might be silly for functions but this pattern comes in handy in different context when trying to mock components and organize code in several files.

Reproduction

https://stackblitz.com/edit/vitejs-vite-q8pc8e?file=main.test.js&view=editor

Simply run the command npm exec vitest to see the issue.

System Info

System:
    OS: Linux 5.0 undefined
    CPU: (8) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 0 Bytes / 0 Bytes
    Shell: 1.0 - /bin/jsh
  Binaries:
    Node: 18.20.3 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 10.2.3 - /usr/local/bin/npm
    pnpm: 8.15.6 - /usr/local/bin/pnpm
  npmPackages:
    vite: ^5.4.3 => 5.4.4 
    vitest: ^2.1.0 => 2.1.1

Used Package Manager

npm

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[sheremet-va]

vi.mock is executed before your imports so you don't have access to them: https://vitest.dev/api/vi.html#vi-mock

If you need to import something during mocking, use import inside the factory:

vi.mock('./deps', async () => {
  const { foobar } = await import( './mock-deps')
  return { foobar }
})

[gabz75]

vi.mock is executed before your imports so you don't have access to them: https://vitest.dev/api/vi.html#vi-mock

If you need to import something during mocking, use import inside the factory:

vi.mock('./deps', async () => {
  const { foobar } = await import( './mock-deps')
  return { foobar }
})

Thanks @sheremet-va, I appreciate your quick response. Is there a reason why some import works? For example, the following works:

import html from 'svelte-htm';

vi.mock('./BookmarkIcon.svelte', () => ({
  default: html`<div data-testid="mock-icon" />`,
}));