Originally Posted by MyFriendIsATaco
I think you are completely missing the point.
Just look at other websites. How do they tailor to multiple resolutions? It's just a matter of observing other peoples' work. No real website out there is tailored for one specific size. It may be optimized for a certain size, but it doesn't look horrible at anything larger.
And no, there is no way that you can just magnify the page to see it in different resolutions, but you don't need to do that. If you make a fluid layout, it's going to work at any size and you don't need to test it.
It's honestly just a matter of looking at other peoples' work. Study what they are doing.