How to test void method in typescript

hey everyone i want to test some code with void method... i have code like this, i very confused with test, i didnt have idea with this test. i make test with jasmine and karma

getMenu(): void {
    this.service.getMenuItems()
    .subscribe(navigation => {
      this.navigationModel = navigation.menu;
    });
  }

this is the code... how i can test this code. everyone who want help me... i hope someone can solve my problem with this test. i have search all with the same problem but i didnt understand. so please help me to solve my testing problem code