Testing my comms before each dive turned into a habit, and it spotted a bad mic before we even got wet.

Smart move. That "testing my comms" habit is such a simple fix for a huge problem. It's like checking your tools before a big job. A bit of static on the surface tells you way more than a garbled yell at 60 feet. I've seen guys have a full regulator mouthpiece crack during a predive check. Catching a bad connection topside just turns it into a minor delay, not a full abort. Those little routines save dives, or worse.