My primary way of ascertaining how bug-free my code is, and the way I've never seen anyone mention, is by feel. Doesn't anyone else roughly know which code is likely to cause bugs and which isn't? Whenever I write some code without thinking it through or take my time, I know it's going to lead to bugs, even if it's very simple.

On the other hand, I have code I wrote that I trust completely. It turns out later that these metrics are, indeed, accurate. Does anyone else get this?