                         it("removes core as subview of fullscreenController") {
                             core.setFullscreen(false)
 
-                            expect(core.fullscreenController.view.subviews).toNot(contain(core))
+                            expect(core.fullscreenController?.view.subviews).toNot(contain(core))
                         }
 
                         it("only set core as subview of parentView once") {

                        it("sets the backgroundColor of fullscreenController to black") {
                            core.setFullscreen(true)

                            expect(core.fullscreenController.view.backgroundColor).to(equal(.black))
                        }

                        it("sets the modalPresentationStyle of fullscreenController to .overFullscreen") {
                            core.setFullscreen(true)

                            expect(core.fullscreenController.modalPresentationStyle)
                                .to(equal(UIModalPresentationStyle.overFullScreen))
                        }



                        expect(callbackWasCall).toEventually(beTrue())
                        expect(core.parentView?.subviews.contains(core)).to(beFalse())
                        expect(core.fullscreenController?.view.subviews.contains(core)).to(beTrue())
                        expect(core.isFullscreen).to(beTrue())
                    }

