ng-mocks not instantiating tested component

I have a Component which I want to test (not mock). It has some public and private fields like destroy$ = new Subject(); which have no @Input. When I call MockRender and get the component via fixture.point.componentinstance, the fields are undefined. A console-log inside the constructor does also not get triggered. So what does MockRender do? Why does it not instantiate the component class in a proper way? Or am I using the lib in wrong way? Is this expected behavior?