Only the code in the class-under-test should be exercised. In case of the CurrentWeatherComponent, we need to ensure that the service code is not executed. For this reason, you should never provide the actual implementation of the service. This is also why we used HttpClientTestingModule in the previous section. Since this is our custom service, we must provide our own implementation of a test double.
In this case, we will implement a fake of the service. Since the fake of the WeatherService will be used in tests for multiple components, your implementation should be in a separate file. For the sake of maintainability and discoverability of your code base, one class per file is a good rule of thumb to follow. Keeping classes ...
