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feat(@jest/globals, jest-mock): add jest.Spied* utility types #13440

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merged 14 commits into from Oct 16, 2022

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mrazauskas
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@mrazauskas mrazauskas commented Oct 14, 2022

Summary

@types/jest provides jest.SpyInstance<T> and jest.SpiedFunction<T> utility types. Jest currently does not exposed these on the jest namespace.

Note that jest.SpyInstance<T> works only on methods, but can’t be used on class constructors, getters and setters. It is equal to jest.SpiedFunction<T> only that jest.SpyInstance<T> takes two type arguments instead of one.

To cover more use cases, I created jest.SpiedClass<T>, jest.SpiedFunction<T>, jest.SpiedGetter<T>, jest.SpiedSetter<T>. Names are similar to jest.Mocked* utilities.

jest.Mocked<T> is very smart type. I wanted to have somewhat similar jest.Spied<T>. It works only with classes and functions, because there is no way to differentiate between a getter and a setter. I mean, either of them would simply have type of string or number not a function signature. Hence user will have to use jest.SpiedGetter<T> or jest.SpiedSetter<T>.

Test plan

Type test added.

@mrazauskas mrazauskas marked this pull request as draft October 14, 2022 04:52
Comment on lines 142 to 146
const utils = jest.createMockFromModule('../utils');

utils.isAuthorized = jest.fn(secret => secret === 'not wizard');
jest
.spyOn(utils, 'isAuthorized')
.mockImplementation(secret => secret === 'not wizard');
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it doesn't make sense to spyOn here - isAuthorized is already a mock function (that's what createMockFromModule does)

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Ups.. This change should not be here. My bad (;

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@SimenB SimenB Oct 16, 2022

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instead of utils.isAuthorized = jest.fn(secret => secret === 'not wizard'); it should probably be utils.isAuthorized.mockImplementation(secret => secret === 'not wizard');

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These lines got autocorrected, because I was playing with jest/prefer-spy-on ESLint rule. I was hoping to find better example for docs, but nothing came out. jest/prefer-spy-on rule will come in later as separate PR (;

@mrazauskas mrazauskas marked this pull request as ready for review October 16, 2022 11:03
@mrazauskas mrazauskas marked this pull request as draft October 16, 2022 11:15
@mrazauskas mrazauskas marked this pull request as ready for review October 16, 2022 11:55

Constructs the type of a spied class or function (i.e. the return type of `jest.spyOn()`).

```ts title="__utils__/setDateNow.ts"
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Now I am happy about the example. The point was to show that typings can be useful in some test util.

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nice!

docs/JestObjectAPI.md Outdated Show resolved Hide resolved
/**
* Constructs the type of a spied class or function.
*/
export type Spied<T extends ClassLike | FunctionLike> = JestSpied<T>;
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this is copied manually, right? Should we set up a script which keeps it in sync with @jest/globals?

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Would be possible, but is it worth it? I mean, these types are only used in Jest repo. If something will be missing, typechecks of tests will catch it for us.

Perhaps some check that these types are still exposed in @jest/globals? Just another type test? Sound simple to do and to run automatically. Together with typechecks of test files that should be enough. I will do this as separate PR. If that’s fine? (;

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Definitely separate 👍

Co-authored-by: Simen Bekkhus <sbekkhus91@gmail.com>
@SimenB SimenB merged commit faef42e into jestjs:main Oct 16, 2022
@mrazauskas mrazauskas deleted the feat-add-jest.Spied-type-utils branch October 16, 2022 14:14
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SimenB commented Oct 18, 2022

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3 participants