Awesome! So glad to here that you sorted it out!
Testing-wise (and automated testing notwithstanding), I tend to test my skills using whatever Echo device is nearby. While you don’t need a real device to test, there’s nothing nearly as rewarding as hearing the results on a real device. I also frequently use the Alexa app on my phone if I don’t have a device nearby (such as when I’m away from home). In short, it sounds like you’ll be able to test with the Kindle Fire, but if you continue to enjoy this kind of thing, I’d recommend a small investment in an Echo Dot or some other device.