Virtual module mocking behavior in Vitest 4

[HiDeoo]

Using a discussion as I'm not sure yet if this is an expected change of behavior, a bug, or just me misusing an API.

In a test file, I have different describe blocks where in each of them, I mock a virtual module, e.g. using vi.doMock() and mock a function from that module making it return different values.

• In Vitest 3, everything seems to work as expected, and calling some code that uses that virtual module returns the mocked value.
• In Vitest 4, the first mocked value seems to be returned for all tests.

I've carefully read the Vitest 4 migration guide, and specifically the section about "Changes to Mocking", but unless I'm missing something, I don't think any of the listed changes explain this behavior.

I've setup a minimal repro here where tests are failing due to unexpected values being returned. When running pnpm add vitest@3 in the same repo, all tests pass as expected.

Thanks for any insights and your time 🙌

[hi-ogawa]

I looks like a bit of edge case, but not sure. From a quick look, it would make more sense to do in the following order with "reset" then "mock". Would this work too or also broken?

    vi.resetModules();
    vi.doMock("virtual:test", () => ({ getFirstNumber: () => 2 }));

[HiDeoo]

I think I may have tried to switch the statements, but just tried it again for sanity, and the behavior is identical:

• Vitest 3: works as expected
• Vitest 4: the first mocked value is returned for all tests

[hi-ogawa]

Can you create an issue?

[HiDeoo]

Sure, will do, thanks for taking a look 🙌