As for phase, use a 1.5 to 9 V battery. Check that when you connect the battery the woofer moves in the same direction on both speakers.
+1, Battery test is simple and effective!
BTW, most multi-way speakers battery test only worked on woofers. Due to the passive crossover, mid-driver and tweeter have to connect the battery across the driver terminals!
IMO, 1.5V battery is better than 9V, 9V DC across a 4-8 ohm driver is way too high.