fix(jest-mock): improve spyOn typings to handle optional properties

[mrazauskas]

Summary

Apparently spyOn overloads do not work properly if an interfaces with optional props is encountered:

interface OptionalInterface {
  methodA?: ((a: boolean) => void) | undefined;
  methodB: (b: string) => boolean;
}

const optionalSpiedObject = {} as OptionalInterface;

spyOn(optionalSpiedObject, 'methodA'); // "No overload matches this call. Etc..."

So this got fixed.

Test plan

Type tests are added.

[mrazauskas]

V is just a helper to avoid SpyInstance<(...args: ConstructorParameters<Required<T>[K]>) => InstanceType<Required<T>[K]>>

[mrazauskas]

methodKey and K are just renames for consistency. MethodLikeKeys, PropertyLikeKeys, methodKey, propertyKey, K – always keys. Easier to understand what is happening.

[mrazauskas]

Lines with Required do all the magic, because they turn types like (() => void)) | undefined into () => void). Something what wasn’t a function, becomes one. This part was not working, otherwise logic is the same.

[mrazauskas]

Default is unnecessary, accessType is always passed:

https://github.com/facebook/jest/blob/052aa67f22834933d986c8fb2a373379408ae5ea/packages/jest-mock/src/index.ts#L1043-L1045

[SimenB]

Nice!

[mrazauskas]

Interestingly same things here DefinitelyTyped/DefinitelyTyped#62208 fails to compile on TS 4.4. But in Jest repo all is fine on TS 4.3. I always have a feeling that to go through CI on DT is simply luck ;D

[SimenB]

https://github.com/facebook/jest/releases/tag/v29.1.0

[github-actions]

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