Testing selectors that use selectors

I have a (dynamic) selector that uses another selector. I thought i could test it with a (fake) state, expecting the tested selector to call the used selector with that state. However i seem to have to test it with data similar to the output of the called selector.

The following code snippet tries to illustrate it:

---

    export class SomeSelectors {

        @Selector([SomeState])
        static getSomethingFirst(state: SomeModel) {
            return state.something;
        }

        static getSomethingSecond(...categories: string[]) {
            return createSelector([SomeSelectors.getSomethingFirst], (somethingsFirst) =>
                ..
            );
        }
    }

    describe('SomeSelectors', () => {
        const someFakeState = {
            something: 'test me'
        };

       describe('getSomethingSecond', () => {
          it('i would like to test it with a fake state', () => {
             const result = SomeSelectors.getSomethingSecond(someFakeState)('test-category');
             expect(result).toBeTruthy();
          });

           it('however i must test it with something that is like ', () => {
               const result = SomeSelectors.getSomethingSecond(someFakeState.something)('test-category');
               expect(result).toBeTruthy();
           });
       });
    });

---

I think i miss some understanding about how these selectors really work. Anyone some pointers on how to see them?