jest.resetModules() can fail when using identity-obj-proxy

[danrr]

🐛 Bug Report

jest.resetModules() iterates over the global object and checks if any properties are mocks by evaluating if globalMock._isMockFunction is truthy for each property on the global. (https://github.com/facebook/jest/blob/949701376f1af75befd1a759aff5ac8080fb33af/packages/jest-runtime/src/index.js#L433)

If using identity-obj-proxyto mock a property on the global object anywhere in the test setup, jest.resetModules will break. identity-obj-proxy is a proxy that returns the key as the value for any attemps to index the object (https://github.com/keyanzhang/identity-obj-proxy/blob/master/src/index.js#L18) which means the value of _isMockFunction will be the string _isMockFunction which is truthy, and the value of mockClear will be the string mockClear which is not a function, ergo the error TypeError: globalMock.mockClear is not a function.

To Reproduce

Steps to reproduce the behavior:

• Set a global property to be identity-obj-proxy
• Call jest.resetModules() during a test

Expected behavior

Test should pass, correct mocks should be cleared

Link to repl or repo (highly encouraged)

https://repl.it/@danrr/SuperNegligibleGeeklog

Run npx envinfo --preset jest

Paste the results here:

System:
    OS: macOS High Sierra 10.13.6
    CPU: x64 Intel(R) Core(TM) i7-7660U CPU @ 2.50GHz
  Binaries:
    Node: 8.11.4 - ~/.nvm/versions/node/v8.11.4/bin/node
    npm: 5.6.0 - ~/.nvm/versions/node/v8.11.4/bin/npm
  npmPackages:
    jest: ^23.4.1 => 23.5.0 

[SimenB]

Interesting! We might want to consider som Symbol to make the check safer.

I've thought that I want to move all properties we attach to a mock behind a symbol anyways, but it's pretty breaking.

@thymikee @rickhanlonii thoughts?

[danrr]

Can the globalMock._isMockFunction check be changed to globalMock._isMockFunction === true to fix this issue in the short term?

[SimenB]

for sure. PR welcome 🙂

[github-actions]

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