So is the usual flow to throw these in places where code shouldn't execute but then create tests to try and trip it up to see if that is truly the case? I would hate to be running a release build with this, or does the compiler do something different depending on build type?

> I would hate to be running a release build with this

The usual argument is that the program would be in an invalid state if the condition was reached, so the only option is to crash. If it turns out it's a valid state, then the programmer can treat in a branch. I don't think tests would capture this because they would operating under the same assumption that such states cannot exist. Maybe fuzzy testing could surface an issue like this.