I always thoroughly playtest my updates, testing every option and every path that I can imagine to be relevant. While it's impossible to detect every bug in a software solution before releasing it to the public, no matter how well you test it, I still manage to make my releases next to bug-free.
Several other high-profile adult game developers usually warn that you should "expect lots of bugs" in their updates, which makes me wonder what the hell they are doing. I have never dared look at their code, for I value my sanity too much. Coding a visual novel-style game in Ren'py isn't something that should normally lead to bug-bonanza.
I
have looked at some developer's code. I'm pretty sure one game (Daddy's Goodnight Kiss) actually made me stupider. He had an event with 3 steps, with a state variable for each step. The possible actions in each step were the same (which girl you talked to). He used numbers instead of defined constants for his states, and the number corresponding to each girl was different in the different stages. Like the girls would be (respecitvely) 1,2,3, then 2,3,1, then 3,1,2. Drove me crazy trying to figure out how to fix the bugs in that and how to get every possible dialog. Plus it was an uncommented mess (he shipped .rpys, not just .rpycs). I have no idea how he understood what his code did when he looked at it the next day.
In my job, I got a bug report about a certain feature. I haven't thought about how I'm going to code the fix, but I've already thought about how I'm going to test it. Testing can be a PITA, but my motto is "if it's not tested, it doesn't work".