For debugging, I’m reminded of Beth Simon et al’s recent Peer Instruction work where she was deliberately constructing examples where students were likely to show a shallow or incomplete model of programming, e.g. they would have problems with loops that start at 1, or go backwards, or have less than vs less than or equal to end conditions. As I understand it, Simon et al said there was a fine art in example construction, to make sure it drew out common student misconceptions so that they could be discussed and corrected/ - https://computinged.wordpress.com/2013/05/13/the-critical-part-of-pck-what-students-get-wrong