There's nothing like testing on the actual device, but in some cases emulators are extremely necessary. For Android I use Genymotion, but at the moment I need some iOS emulator so that it can test the basic compatibility of an application developed in Xamarin.
Is there an iOS emulator that does not need an actual device and runs on Windows or Linux?
In this case I'm using Visual Studio and Xamarin, the other questions that were related to this refer to Ionic / Cordova.