Set resetMocks to true by default

[EmmanuelDemey]

🚀 Feature Proposal

As described in the thread https://twitter.com/kentcdodds/status/1182744387190607872, we should set resetMocks param to true by default.

Motivation

In order to make our tests isolated.

Example

thanks to this new default value, we won't have to define afterAll method in our unit tests, in order to reset something.

afterEach(() => {
  jest.clearAllMocks()
})

Pitch

This feature is part of the core project . https://jestjs.io/docs/en/configuration#resetmocks-boolean. This change will make de developer experience smoother when writing unit test with jest.
As writing isolated test is a good practice, we should make it easy to implement, without writing extra code.

Why does this feature belong in the Jest core platform?

Common feature proposals that do not typically make it to core:

• New matchers (see jest-extended)
• Changes to the default reporter (use custom reporters instead)
• Changes to node/jsdom test environments (use custom environments instead)

[github-actions]

This issue is stale because it has been open for 1 year with no activity. Remove stale label or comment or this will be closed in 14 days.

[bozdoz]

Note the proposal does not match the example. resetMocks is not equal to clearAllMocks

clearAllMocks clears calls, instances, and results (and this is a good thing to do!): https://jestjs.io/docs/jest-object#jestclearallmocks

resetAllMocks is what is called by setting resetMocks to true; and this does what clearAllMocks does, but also removes implementations and mocked return values (and this is not a great thing to do!): https://jestjs.io/docs/configuration#resetmocks-boolean

Justification: clearing all mocks is great, because tests should be isolated (thanks @kentcdodds). Resetting all mocks is generally bad, because you will make manual mocks useless (also see #10419), and make useless any other mock implementation that a developer may have created for a test suite (solution to the latter is to re-implement it in a beforeEach, but there shouldn't be a need to do this)

I would propose to close this ticket, and keep resetMocks default as false

[drFabio]

Is there any viable solution to restore manual mocks?

Having reset on a beforeEach makes them look like they could be only used once. Looks like with this reset clearing the manual we have no use for manual mocks that can have a different implementation

[jeppester]

@bozdoz @drFabio
I made the following PR a long time ago, which unfortunately got stuck somewhere:
#9270

It makes each mock remember it's initial implementation and provides a way to restore the initial implementation.

I believe it would be a very viable solution to restoring manual mocks, and that it would be a safer and better way to reset the state between tests than resetAllMocks or restoreAllMocks.

[github-actions]

This issue is stale because it has been open for 1 year with no activity. Remove stale label or comment or this will be closed in 30 days.

[github-actions]

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