... Is there anyway to test how round they are?
You could just watch them in play, but if you really want to test them...
Place a ball on the head spot. Put the number on top and turned so you can read it from the end rail. Lag it down and back to try to leave it on the head spot. Watch for roll-off to the left or right.
Do the test again but with the number turned so you can read it from the side rail.
Do the test again but with the numbers on the sides as the ball rolls down the table.
Repeat for each ball.
Balls can be out of round or out of balance. Cyclop brand balls went out of business because a significant percentage of their balls -- 1in 200? -- were out of balance and might roll off six inches on the lag.
Few people have the patience to do the test above. It's easier to just watch the balls in play. Pay attention to what they do as they roll to a stop.