Hello. I plan on continuing the series with other parts of testing; Capybara, FactoryGirl, Mock, CI, CD, etc.

It does work with Rails 5! I've had luck with it, but you will want to make sure that you have pretty good test coverage to make sure stuff doesn't break. Goldiloader is pretty awesome, but it does add a bit too much 'magic'. The proper/better solution is to fix the performance gaps in the code rather than relying on the gem. However, if you do want to give it a shot, I've had luck with v0.0.12 and still getting passing tests. I think there was an issue on v2.0.0. It might have since been resolved.

Hello Drilon, I do not work with PayPal. I disagree with a lot of their practices and chose not to support them. I found that they work well whenever there are no problems, but when a problem did occur, the merchant and buyer both lost and only PayPal benefited.

This is common and typically due to the validation failure handling of 

render :new

Have a look at https://stackoverflow.com/a/41520362/722274

One way around this is to do client side validations which I have an example of this at https://www.driftingruby.com/episodes/client-side-validations

You could mix and match based on the complexity of the JS needed. You could also look at something like client side validations to prevent the form from posting if the data isn’t valid (but not recommended for uniqueness validations because of potential security reasons).