In order to test components and services which depend on router navigations, such as `ActivatedRoute` instances, tests currently need to provide a fair bit of boilerplate _or_ they can set up a stub for `ActivatedRoute` and list it in the `providers` to override it in `TestBed`. This approach of stubbing the `ActivatedRoute` creates a situation that can easily cause the test to break. The stub often only mocks out the dependencies that the component/service _currently_ needs. This dependencies might change over time and break the test in an unexpected way. In addition, it is difficult to get the structure of `ActivatedRoute` exactly correct.
This change will allow unit tests to quickly set up routes, trigger real navigations in the Router, and get instances of component's to test along with real instances of `ActivatedRoute`. This all comes without needing to know that the component depends on `ActivatedRoute` at all. This becomes more important when considering that a component may be refactored in the future to use `@Input` rather than access data on the `ActivatedRoute` instance (see #18967). Tests which mock out `ActivatedRoute` would all break, but those which use `navigateForTest` would continue to work without needing any updates.
resolves#15779resolves#48608
PR Close#48552
