You can run Gnome Web for free. It's the open source version of WebKit so you won't be able to see all the tweaks Apple adds to their proprietary build, but it's close enough that obvious differences are visible, at least on desktop.
Safari on iOS cannot be tested without paying Apple so I generally don't for my personal stuff either.
All of that said, American developers often can't even be bothered to support characters like ñ or é, so I think it's quite reasonable to expect an EU browser to be a second class citizen for American developers. We can work around that pretty easily by simply not buying products and services that don't work well in the EU.
Safari on iOS cannot be tested without paying Apple so I generally don't for my personal stuff either.
All of that said, American developers often can't even be bothered to support characters like ñ or é, so I think it's quite reasonable to expect an EU browser to be a second class citizen for American developers. We can work around that pretty easily by simply not buying products and services that don't work well in the EU.