A colleague showed me this yesterday:
Read the on-screen output, wait a few seconds then run
Here's me having a crack at it.
Not quire sure why there is such a discrepancy in the length, and this example is a crossover cable worked out by MDIX and is part of an etherchannel group.
This was on a 2960S with 12.55 IOS. I believe the command was introduced somewhere around 12.2.
Anyway, just thought I'd share. It could be handy if you're caught short without a cable tester, or you need to test cables remotely ;)
There are lots of other things to test here:
Binary is as easy as 01 10 11