No person can truly know both sides of that equation. Having been on the wrong side of it, I can only testify that I wish I had waited and never 'known' anyone before I married. My view now (a half-life later) is that an unmarried Christian couple does well to avoid
anything overtly sexual and many activities in the "non-sexual intimacy" category
The test drive idea is (expletive!) from the mind of the enemy and the evil heart of humans. Someone who suggests it is revealing their disrespect of their partner and their own selfishness. Someone who loves in a biblically-sound way will accept their new spouse completely, regardless of flaws. Nobody is perfect, so instead of hoping for or expecting perfection, rather we should expect a spouse to be incomplete and partly broken, in need of grace and much love.
I can't quantify this or quote chapter and verse to support it, but I believe that sex prior to marriage (for either partner or both together) takes something away from a couple's experience within marriage, perhaps in ways they will never know. At the least, they will be left comparing or wondering what if... both are destructive. Marriage is God's design, and if you change the order of assembly, something isn't going to work quite right.