You can tell a male and female apart by their fins. Males have much longer fins. If you've ever seen a picture of a betta with those beautiful, flowing fins, it's a male.
So the question is: does he/she have long fins, or short ones? If short, then you have a little female. I don't believe there are many exceptions to that unless he/she is very young.
As for the water testing, if you've had him for awhile and he was acting fine, it might not be necessary. I haven't tested the water for my betta and he's been great for close to two months. At the same time it can't hurt to rule anything out.
Does it looks like he's having trouble swimming up to the surface? Like he wants to be up there but he sinks back down, or does he seem to do it himself?
As for the water testing, if you've had him for awhile and he was acting fine, it might not be necessary. I haven't tested the water for my betta and he's been great for close to two months. At the same time it can't hurt to rule anything out.
Does it looks like he's having trouble swimming up to the surface? Like he wants to be up there but he sinks back down, or does he seem to do it himself?