How big of a swatch for socks? Does it need to be done in the round?
It should be done in the round…
you can do fake rounds (large I-cord type knitting)
I am a very good knitter, (and almost never row out!) but i know my gauge is different when i Knit 1 row, Purl 1 row. (the purl rows are ever so slightly looser!)
and this small difference does effect gauge!
(i sometimes knit 1 row, and then backwards knit the next row–and surprizingly, my backwards knitting is closer in gauge to regular knitting than my purling is…
One advantage of toe up socks is you can use the first inch or so (the toe!) as a gauge swatch… (if too tight, a few more rows will resolve (the fit) if too loose, a smaller needle will have the foot fitting fine (and the slightly loosely knit toe won’t matter!)