chore: extend and improve type tests for `jest` object #12442

mrazauskas · 2022-02-20T19:57:04Z

Resolves #10118
Resolves #10200

Summary

While working on jest-mock types, I noticed that isMockFunction and spyOn are not covered by type tests. So I though it would be better to type tests before refactoring anything to be sure that nothing breaks.

Interesting find. Apparently api-extractor broke isMockFunction types exposed from jest-environment. Just look at the build .d.ts. The return type of isMockFunction is fn is unknown. This is fixed. Also I added an improvement to isMockFunction typing inspired by #10118. Covered by tests. Will leave an inline comment.

The #10200 is puzzling case. It appears that all types referenced there are living inside @types/jest. Despite that this is great case for typing and testing. spyOn function in Jest repo was missing one overload, but @types/jest had it. This is the overload catching a class (e.g., Date class from the issue). I placed the class overload just above the one which is catching a function. That’s the only difference from @types/jest, but it solves the issue mentioned by the user. Included in tests.

Of course, I went through the test suite in @types/jest. Adapted what seemed useful.

Tests for Mock Functions are still missing. These will follow soon with another PR.

Test plan

New and old tests should pass.

mrazauskas · 2022-02-20T19:59:40Z

packages/jest-mock/src/index.ts

+  isMockFunction<T, Y extends Array<unknown> = Array<unknown>>(
+    fn: (...args: Y) => T,
+  ): fn is Mock<T, Y>;
+  isMockFunction(fn: unknown): boolean;


The first overload will infer return type and types of args if a function is passed. Second one allows to pass any value. This way types do the same job as before, but with added feature.

should second be isMockFunction(fn: unknown): fn is Mock<unknown, unknown> instead?

In this case, if string is passed the typed in if (isMockFunction(someString)) looks like this:

No harm at all, because this branch will not execute anyway. Simply seemed unnecessary. So boolean looked like cleaner solution.

what if hardlyMock is any or unknown?

These are good edge cases. I added tests

right, and then isMockFunction(fn: unknown): fn is Mock<unknown, unknown> still doesn't help in setting the correct type in the if?

mrazauskas · 2022-02-20T20:09:00Z

packages/jest-types/__typetests__/jest.test.ts

+  expectType<Mock<boolean, [a: string, b: number]>>(maybeMock);
+
+  maybeMock.mockReturnValueOnce(false);
+  expectError(maybeMock.mockReturnValueOnce(123));


TS is wrapping the function in Mock type here. I think that’s fine, this branch will never run anyways.

mrazauskas · 2022-02-20T20:09:42Z

packages/jest-types/__typetests__/jest.test.ts

+if (!jest.isMockFunction(hardlyMockFn)) {
+  expectType<string>(hardlyMockFn);
+}
+
+if (jest.isMockFunction(hardlyMockFn)) {
+  expectType<string>(hardlyMockFn);
+}


Works if value is not even a function.

mrazauskas · 2022-02-20T20:17:01Z

packages/jest-types/__typetests__/jest.test.ts

+expectType<SpyInstance<Date, [value: string | number | Date]>>(
+  jest.spyOn(global, 'Date'),
+);


With @types/jest this is failing, but passing here (;

mrazauskas · 2022-02-20T20:47:32Z

packages/jest-mock/src/index.ts

@@ -1003,27 +1014,34 @@ export class ModuleMocker {
    return fn;
  }

-  spyOn<T extends {}, M extends NonFunctionPropertyNames<T>>(
+  spyOn<T extends object, M extends NonFunctionPropertyNames<T>>(


{} as a constrain type allows any non-nullish value. See typescript-eslint/typescript-eslint#2063 (comment). Here it is almost the same as any, because string or boolean are allowed. Might be better to use object (any non-primitive value).

mrazauskas · 2022-02-20T20:53:43Z

packages/jest-types/__typetests__/jest.test.ts

+expectType<SpyInstance<boolean, [arg: any]>>(
+  jest.spyOn(spiedArray as unknown as ArrayConstructor, 'isArray'),
+);
+expectError(jest.spyOn(spiedArray, 'isArray'));


Errors, because TS does not see isArray method without type casting.

SimenB

yay, this is awesome!

SimenB · 2022-02-21T08:19:16Z

Interesting find. Apparently api-extractor broke isMockFunction types exposed from jest-environment. Just look at the build .d.ts. The return type of isMockFunction is fn is unknown.

Might be worth reporting a bug

mrazauskas · 2022-02-21T08:28:13Z

packages/jest-mock/src/index.ts

@@ -995,7 +995,7 @@ export class ModuleMocker {
  isMockFunction<T, Y extends Array<unknown> = Array<unknown>>(
    fn: (...args: Y) => T,
  ): fn is Mock<T, Y>;
-  isMockFunction(fn: unknown): boolean;
+  isMockFunction(fn: unknown): fn is Mock<unknown>;


@SimenB Might be this is better idea. See tests. Thanks for good questions!

perfect, thanks!

SimenB · 2022-02-21T08:35:04Z

packages/jest-types/__typetests__/jest.test.ts

-expectType<typeof jest>(jest.useRealTimers());
+expectError(jest.unmock());
+
+// Mock Functions


should we have these tests in jest-mock, and just have an expectType<JestMock['fn']>(jest.fn) and expectType<JestMock['isMockFunction']>(jest.isMockFunction)? Gut feeling is that's more natural since at the jest.* level it's more of an integration test and not a "unit".

Of course, doesn't really matter, but the tests would be closer to the code it tests

That's good idea. I will move them but later, not at computer right now. Also tests for Mock Function fits better in jest-mock.

Cool, thanks! Let's land this in the meantime 🙂

github-actions · 2022-03-24T00:06:52Z

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add type tests for jest object

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mrazauskas commented Feb 20, 2022

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fix test

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tweak constrain

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mrazauskas commented Feb 20, 2022

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mrazauskas changed the title ~~chore: add type tests for jest object~~ chore: extend and improve type tests for jest object Feb 20, 2022

SimenB approved these changes Feb 21, 2022

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mrazauskas added 5 commits February 21, 2022 08:37

add changelog entry

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clean up

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clean up

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real clean up

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more tests

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tweak overload type

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mrazauskas commented Feb 21, 2022

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SimenB approved these changes Feb 21, 2022

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SimenB reviewed Feb 21, 2022

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SimenB merged commit 7a05a6c into jestjs:main Feb 21, 2022

mrazauskas deleted the feat-jest-object-type-tests branch February 21, 2022 12:31

This was referenced Feb 21, 2022

chore: run type tests using old version of TS #12449

Merged

chore: add type tests for Mock Function #12459

Merged

SimenB mentioned this pull request Feb 27, 2022

Introduce a more flexible and better typed way to mock APIs #7832

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chore: extend and improve type tests for `jest` object #12442

chore: extend and improve type tests for `jest` object #12442

mrazauskas commented Feb 20, 2022

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chore: extend and improve type tests for jest object #12442

chore: extend and improve type tests for jest object #12442

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mrazauskas commented Feb 20, 2022

Summary

Test plan

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SimenB Feb 21, 2022 • edited

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github-actions bot commented Mar 24, 2022

chore: extend and improve type tests for `jest` object #12442

chore: extend and improve type tests for `jest` object #12442

SimenB Feb 21, 2022 •

edited