Mocking is lost when threads: false is set

[EvHaus]

Describe the bug

I'm seeing a strange behavior with threads: false which might be related to #468 and #294. When you mock modules, the mocking works on initial run, but mocks are reset to undefined when watch mode refreshes, or the when another suite runs.

Reproduction

Use this tiny repro suite where I mock the ora package: https://stackblitz.com/edit/node-72ecu4?file=index.ts

To reproduce the problem, run the stackblits as normal. You'll notice the initial run works without any issues.

Then make any edit to any file (ie. add some white space) to trigger watch mode to re-run the tests. You'll see that the tests now fail with:

TypeError: Cannot read properties of undefined (reading 'start')

This is because the ora mock somehow becomes undefined.

System Info

System:
    OS: macOS 12.1
    CPU: (8) x64 Intel(R) Core(TM) i5-8279U CPU @ 2.40GHz
    Memory: 32.75 MB / 16.00 GB
    Shell: 5.8 - /bin/zsh
  Binaries:
    Node: 16.13.1 - ~/.nvm/versions/node/v16.13.1/bin/node
    Yarn: 1.22.17 - /usr/local/bin/yarn
    npm: 8.1.2 - ~/.nvm/versions/node/v16.13.1/bin/npm
    Watchman: 2022.01.03.00 - /usr/local/bin/watchman
  Browsers:
    Chrome: 97.0.4692.71
    Chrome Canary: 99.0.4813.0
    Firefox: 95.0
    Safari: 15.2

Used Package Manager

npm

Validations

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• Read the Contributing Guidelines.
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• The provided reproduction is a minimal reproducible example of the bug.

[sheremet-va]

This is kinda an experimental fix. I remember why we added that line, but locally all is fine after removing it.

Let me know if it adds new issues :S

[EvHaus]

Seems to be working well for me. Thank you!