How to unit test a function that uses the new Angular 14's "inject" function?

I've created a function that utilizes that new Angular 'inject' function. Since the inject function can be used only when initializing a class (or factory) that is part of the dependency injection tree, this function is meant to be used in the constructor of a component / service.

I want to unit test this function with mock dependencies. The problem is I can't just call it in unit tests, because it will be called in an incorrect context. I can create a component / service just for the unit test purposes but it feels like too much boilerplate to test a simple function.

Is there a recommended way of doing this?

I know it's been a while, but I finally thought of a solution that is elegant enough to be the standard way of doing it.

Let's assume the function you want to test is myInjectionFunction:

// This is a utility function you can put in a shared place and use it whenever you want
function useInjectionFunction<GArgs extends any[], GReturn>(injectionFunction: (...args: GArgs) => GReturn, injector: Injector) {
  const token = new InjectionToken<GReturn>(injectionFunction.name);
  return (...args: GArgs) => Injector.create({
    parent: injector,
    providers: [
      {
        provide: token,
        useFactory: () => {
          return injectionFunction(...args);
        },
      },
    ],
  }).get(token)
}

describe('My Test suite', () => {
  let myFunction: typeof myInjectionFunction;

  beforeEach(() => {
    TestBed.configureTestingModule({
      // configure your providers here
    });

    myFunction = useInjectionFunction(hasFeatureFlag, TestBed.get(Injector));
  });

  it('should work', () => {
    // call "myFunction" regularly to test it
  });
});

Leaving it here if anyone wants to use it.