The battery test is easy to do. I use a 1.5 volt AA battery instead of a 9 volt battery with the snap terminals on top. 1.5V is enough juice to see the mid range cone move backward or forward.
Years ago when I built my CAOW1 speakers, I goofed on the polarity. The 2nd order design of that 2-way calls for the woofer-to-tweeter crossover to be in opposite polarity. I built it over a weekend and several week nights back when I was also going to work every day. When I wired up the XO board, I included the polarity reversal for the tweeter, and then promptly forgot that I did it. Later, when I assembled everything, I switched the polarity again when I attached the XO to the tweeter.
Some time later Dennis heard them, and asked me if I'd like him to measure them. He already knew I had goofed, but his measurement easily showed it. He was too polite to say it to me directly.
So, don't be afraid of what you find out. It's better to goof, find it, and fix it than to goof and think you're a genius who got everything right the first time.