How can we test Roku application

I'm new to Roku development (in R&D phase actually). I read that we can't test Roku app on simulator and need real device. If we develop an application, how will we test it?

I checked Roku developer site and different links on internet, but could not find anything that answers my questions

As per my info, Roku sells 5 devices so:

• Can we do one app that supports all 5 devices?
• Do we need assets in multiple resolutions?
• Do I need to buy all devices?

Please help. Thanks