`waitFor` doesn't advance time when using `jest` fake timers without injecting globals

[signorettif]

• @testing-library/dom version: 9.3.4
• Testing Framework and version: [email protected]
• DOM Environment: [email protected]

Relevant Code or Config:

A minimal sandbox to reproduce the issue is available on codesandbox. You can execute tests by opening a terminal and running the yarn test command.

Actions Undertaken:

• Configured jest to not inject globals (--injectGlobals=false); refer to the package.json command from the sandbox above.
• Created tests that rely on waitFor or waitForElementToBeRemoved.

Outcome:

• waitFor never advances timers by time (the default 50ms interval of the loop or any other interval), causing the tests to exceed their timeout.

Reproduction:

You can reproduce this issue via the following codesandbox link.

Problem Description:

When using jest, but without injecting globals, the waitFor logic:

• Fails to identify jest's environment in the jestFakeTimersAreEnabled predicate.
• Assuming the above was passing correctly, it would reference the jest global object, which is undefined when not injecting globals. This would lead to an error when attempting to invoke jest.advanceTimersByTime.

On a broader scope (although I want to keep this issue's focus narrow for the sake of actionability), there might be other unintended implicit assumptions about depending on (a) jest and / or (b) a test environment that injects globals. The following issues are related, although they focus on different manifested problems:

• https://github.com/testing-library/react-testing-library/issues/1240
• https://github.com/testing-library/react-testing-library/issues/1257

Suggested Solution:

• The first part of the issue (i.e., jest environment detection) can be resolved by adding an OR condition to the jestFakeTimersAreEnabled predicate. In my experience, we should add a check for process.env.JEST_WORKER_ID to not be undefined.
• The second issue could be addressed by dynamically attempting to import jest from @jest/globals when (a) we detect a JEST_WORKER_ID and (b) we know fake timers are enabled.
  • I don't believe dom-testing-library should depend on @jest/globals.
  • I'm not completely satisfied with the tentative dynamic import of an optional dependency @jest/globals in this case, but I think it might provide the best developer experience for end users.

Depending on the appetite for this issue to be fixed, I might work on a PR to address the above. I am somewhat surprised this hasn't come up before, but I guess not many people tend to set up jest without injecting globals.

[krutoo]

@signorettif May this ussue be relative to this problem? https://github.com/testing-library/user-event/issues/1173

[signorettif]

Yes! I think that's a symptom of the same underlying problem