fix(mock): allow to mock methods in getters

[SomaticIT]

Summary

In TypeScript 3.9.x, module "re-export" is done using readonly accessor.
It breaks all tests written using jest.spyOn mocks.
A solution is to automatically mock methods that are wrapped in getters.

Test plan

/**********************
 * module-a
 **********************/

// file: lib/feature.ts
export function myFunction(): boolean {
    return true;
}

// file: index.ts
export * from "./lib/feature.ts"

/**********************
 * submodule
 **********************/

// file: lib/subfeature.ts
import * as mod from "module-a";

export function mySubFunction(): boolean {
    return mod.myFunction();
}

// file: lib/subfeature.spec.ts
import * as submod from "./subfeature";
import * as mod from "module-a";

describe("mySubFunction", () => {
    let spy: jest.SpyInstance;
    beforeEach(() => { spy = jest.spyOn(mod, "myFunction"); });
    afterEach(() => { spy.mockRestore(); });

    it("should call mod.myFunction()", () => {
        submod.mySubFunction();
        expect(spy).toHaveBeenCalled();
    });
});

If module-a was built using TypeScript < 3.9, this will work.
If module-a was built using TypeScript >= 3.9, this will throw with error TypeError: Cannot set property query of #<Object> which has only a getter.

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[SimenB]

Don't we support this already via the third option?

https://jestjs.io/docs/en/jest-object#jestspyonobject-methodname-accesstype

[SimenB]

@SomaticIT ping 🙂

[SomaticIT]

@SimenB

The third option, allows to replace the get accessor function of a property.

In my case, we want to change the function which is returned by the get accessor function.
It's an edge case which happens when compiling the code using TypeScript >= 3.9.

So the difference:
object > property > get > function

• accessType option: target the get
• my fix: target the function

This fix allows to easily handle this case with no overhead for the user.

[SimenB]

Aha! Yeah, I think this makes sense, then. Mind giving this a quick rebase (or merge in master)?

[SomaticIT]

@SimenB
Rebase done!

[SimenB]

Thanks!

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