refactor(jest-mock)!: change the default jest.mocked helper’s behaviour to deep mocked

[mrazauskas]

Split from #12727

Summary

It seems to me that by default jest.mocked() should wrap the deep methods of passed object. Currently it requires and argument: jest.mocked(someObject, true). Also note that without reading the docs it isn’t clear what true does.

---

Consider this example:

import { expect, jest, test } from "@jest/globals";
import { someObject } from "./someObject";

jest.mock("./someObject");

test("is mock function?", () => {
  expect(jest.isMockFunction(mockObject.one.more.time)).toBe(true);
});

The test will pass. Seems like jest.mock() is mocking deeply nested methods. So I think jest.mocked() should do the same by default (and jest.Mocked<T> as well).

Possibly shallow mocked definitions were implemented to improve performance of TS compiler. Or to work around some limitation, i.e. handling of recursive types. If I got it right, ts-jest implemented jest.mock() in the early days of TypeScript v3. Performance and handling of recursive types improved a lot in TS v4.

Perhaps it’s time to swap the defaults? I mean, to make the behaviour of jest.mocked() deep by default and to allow opting out with an option: jest.mocked(someObject, {shallow: true}).

Test plan

Type tests added.

[SimenB]

Mye only question is:

import thing from 'thing';

jest.mock('thing');

const mockedThing = jest.mocled(thing);

Would thing be equivalent to mockedThing? Or would they be different? I.e. would one be deep (assuming thing has deep objects) and one the opposite?

[mrazauskas]

Current behaviour:

The test is passing. Hence mockedTime is a mock function, but jest.mocked() didn’t type it as such (needs true to be passed).

Swapping the defaults makes this example work without type errors. Behaviour becomes aligned between jest.mock() and jest.mocked(). Is this what you are asking? (;

[SimenB]

Swapping the defaults makes this example work without type errors. Behaviour becomes aligned between jest.mock() and jest.mocked(). Is this what you are asking? (;

Yep!

[SimenB]

this looks wrong - a type import will fail the typeof below. But why not keep the node-fetch import?

[mrazauskas]

Hm.. Checked it. type works, TS does not complain. Similar to the above: https://github.com/facebook/jest/blob/2f4340cb1da435a9b147e238f7034f99653b8070/docs/MockFunctionAPI.md?plain=1#L500-L505

I was not happy that ESLint (import/order) is pushing to keep 'fetch' import above '@jest/globals'. Probably some ignore comment could fix this.

[SimenB]

awesome, thanks!

[SimenB]

https://github.com/facebook/jest/releases/tag/v29.0.0-alpha.6

[mrazauskas]

Just checked. The example from #13125 (comment) now does not give any type error. Sweet. Thanks!

[SimenB]

https://github.com/facebook/jest/releases/tag/v29.0.0

[github-actions]

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