Observable error problem

gistfile1.txt

//update: Adding async on the subscribe does the trick... 
it('should call observable', () => {
    let mockFn = jest.fn();
    mockFn.mockImplementation(() => {
        return of(4)
    });
    mockFn().subscribe(async (res) => {
        console.log('RES', res); // it logs 4
        await expect(res).toEqual(8);
    });
});

//
//This one will pass
//
it('should call observable', () => {
   let mockFn = jest.fn();
   mockFn.mockImplementation(() => {
            return of (4)
   });
   mockFn().subscribe(res => {
            console.log('RES', res); // it logs 4
             expect(res).toEqual(8);
   });
});

//
//this one will fail correctly
//
it('should call observable', () => {
    let result;
    let mockFn = jest.fn();
    mockFn.mockImplementation(() => {
        return of (4)
    });
    console.log('I am before')
    mockFn().subscribe(res => {
        console.log('RES', res);
        result = res;
    });
    expect(result).toEqual(8);
});