Our candidate found us via a college campus job fair and was given a Codility test for screening. He didn't do particularly well, but got through and, unfortunately, was given another Codility test by mistake.
I suppose he got upset at that point and just copied the solutions from a friend, who was also applying(we only had four sets of questions). That score was of course considerably higher, even though he made the exact same mistakes his friend did.
We found out what was going on and had reservations whether to continue with the process, but he was invited to the second round and aced it.
I think he spent around a year with us and left for a much better paid position.
Overall that Codility test was wholly unnecessary (both the first and the second) and got me thinking how many talented people never made it to the second round because of it.
EDIT: I checked that candidate's current LinkedIn profile and at the moment he's a Tech Lead at globally recognized big data analytics company.