Browser mode: vi.mock in a setup file doesn't work for static imports #11519

Describe the bug

I mock a module in my setup file:

// setup.ts
import { vi } from "vitest";

vi.mock("./weather.ts", () => ({ getWeather: () => "sunny" }));

And use it in a test:

// static.test.ts
import { expect, test } from "vitest";
import { getWeather } from "./weather.ts";

test("gets the mock from the setup file", () => {
  expect(getWeather()).toBe("sunny");
});

In browser mode this fails. The test gets the real module:

AssertionError: expected 'rain' to be 'sunny'

It does work if I use await import("./weather.ts") in the test, or if I add a vi.mock to the test file itself.

It worked in 4.1.11 and 5.0.0-beta.6. It fails every time in 5.0.0 and 5.0.3.

It looks like the test file is imported before the mock from the setup file is ready. #11450 reported the same thing, but the author closed it and it isn't fixed.

I have a small fix with a test and will open a PR.

The text is in my own words. Opus 5.5 found the fix, made the reproduction and posted this for me, reviewed by Fable 5.1.

Reproduction

https://github.com/kasperpeulen/vitest-setup-mock-repro

pnpm install && pnpm exec playwright install chromium && pnpm test

System Info

  System:
    OS: macOS 26.5.1
    CPU: (10) arm64 Apple M1 Pro
  Binaries:
    Node: 24.18.0
    pnpm: 11.28.2
  Browsers:
    Chrome: 155.0.8059.39
  npmPackages:
    @vitest/browser-playwright: 5.0.3 => 5.0.3
    vitest: 5.0.3 => 5.0.3

Used Package Manager

pnpm

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