You can discern those through thinking, too. "Well, it got to this point and broke... hm... well, what do I know about this environment at this point. What assu

You can discern those through thinking, too. "Well, it got to this point and broke... hm... well, what do I know about this environment at this point. What assumptions am I making? Since this assumption isn't being fulfilled, it must be this issue... and that was caused here" Also, this was pair-programming, both people are making sure that what's written is what's intended to be written and so those issues should be (mostly) gone.