Or you could just visually inspect it LOL.
Anyway, to hopefully put this thread out to pasture, I was at the Apple Store the other day to pick up a watch band and decided to check basically every model laptop in the store for this quote-unquote problem. And guess what, they all exhibited a slight gap to some extent or another. Old Airs and new Airs, old Pros and new Pros, they all had some version of this "problem." Definitely tougher to detect with the midnight Air but it was there.
So, unless yours has a truly huge gap that would likely be an issue with the hinge or the entire enclosure itself and thus a real manufacturing defect, this is all a big nothing burger.
I prefer the tap method as many (if not most) lids will have some sort of small
visual gap - that's normal if it's slight and it doesn't mean that the lid won't sit flush and will have give.
It's when the gap 'gives' while tapping the lid while closed that is an issue for
me. But, even when that happens it doesn't mean that the lid will spring open, the magnetic connection still works, it's just what each person cares to tolerate. It's only a nothing burger if it doesn't bother the machine/device owner(s).
Just like the reported light bleed on the M2 Air. It's very common, does not hamper day to day usage and is hard to see in well lit rooms, but if the fact that it's there it's bothersome, especially knowing that there are many M2 Air displays that don't have this issue, it will present as a problem for
some people.
Apple charges a premium for their products - a premium I gladly play. But if someone doesn't feel as though the quality of a product is where it should be, they should return it. If there is a pattern with returns and exchanges, I am sure Apple will take notice and address possible quality control issues with some assembly lines.
And yes, returns/swaps can be a never ending cycle and the next one may have other issues. For me, if the display, keyboard, and build quality are good, I will let other things slide.