I have a RubyMotion iOS app and watch app. The project root contains the iOS and a subdirectory my_watch_app contains the watch app. I followed the guide. Everything is good except for when I try to run the watch app with rake watch. It says it cannot find a simulator device. The main app runs fine.
[!] Cannot find any simulator devices, please add devices in Xcode -> Window -> Devices.
UPDATE To clarify: I had watches paired with devices already. Running rake watch --trace showed that RubyMotion could not resolve a watch to use.
I ended up deleting all simulators that Xcode 10 creates by default and trying with an iPhone 6s. In my case, the default simulator that wanted to run was the iPhone 6s but I deleted it to use an iPhone 8 by default. I kept pairing watches with the device until I found that the Apple Watch Series 2 42mm worked.
I am only able to run watch apps by pairing Apple Watch Series 2 42mm to a simulator.
I can run different simulators using device_name and specifying the iPhone device (RubyMotion launches the iPhone and Watch app at the same time). Again, the device specified must have a Apple Watch Series 2 42mm paired to be able to run rake watch device_name="{{DEVICE}}".
For my iPhone 6s simulator with a Apple Watch Series 2 42mm
rake watch device_name="iPhone 6s"
For my iPhone 8 simulator with a Apple Watch Series 2 42mm
rake watch device_name="iPhone 8"