Should I pay for developer account if I am using it for testing only?
Apple Developer Account
This is my suggestion. If you need to test on a physical device for personal use, then don't pay for a developer account. But if the test needs to be run on multiple devices let's say, showing the app to a client. Then I will say, go in for the paid developer account.
You can test on your device with a free account. But you'll probably have to reload every week. So the question is: what will you do with your app later, once tested ?
? no !