vi.mock() removes functions from classes

[Kjir]

Describe the bug

When mocking a module with vi.mock("./some/module"), some unexpected behaviour happens: classes exported by the module won't have the correct functions when instantiated.

Reproduction

https://stackblitz.com/edit/vitest-dev-vitest-8vqu9r?file=test/basic.test.ts

The same code (transformed in CommonJS format) works with jest, which is creating an inconsistency when migrating (cfr. #1521 )

System Info

System:
    OS: Linux 5.18 Arch Linux
    CPU: (24) x64 AMD Ryzen 9 5900X 12-Core Processor
    Memory: 5.16 GB / 15.51 GB
    Container: Yes
    Shell: 3.4.1 - /usr/bin/fish
  Binaries:
    Node: 16.15.1 - ~/.nodenv/shims/node
    Yarn: 1.22.19 - /usr/bin/yarn
    npm: 8.5.5 - ~/.nodenv/shims/npm
  Browsers:
    Brave Browser: 102.1.39.122
  npmPackages:
    vite: ^2.9.9 => 2.9.12
    vitest: latest => 0.15.2

Used Package Manager

npm

Validations

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[nieyuyao]

We got a new function fn by calling the spyOn when mocking class. But fn.prototype is not set to point to class.prototype? Does it seem like a problem with tinyspy?

[sheremet-va]

We got a new function fn by calling the spyOn when mocking class. But fn.prototype is not set to point to class.prototype? 🤔

🤔

The logic when auto mocking is not quite right. I'm thinking if we maybe should follow jest's approach and collect "metadata" for an object and then recreate it? Right now it just takes all properties (including prototype) and reassigns them, and then also puts original prototype on top of it 🤔 Doesn't seem to be reliable.

If someone has time and ideas on how to improve auto mocking, please, open a discussion or PR 😄

[simon-abbott]

I put up a PR fixing this! #1648