If it didn't cleanly compile and run on linux, it was a autofail. I found a discrepancy in MPICH2 the hard way: it would correctly implement my leader election on my mac, and on my little raspberry pi, but not on a Solaris linux!
Once, I implemented an interpreter/compiler for a toy-language in Opal (a functional language developed and maintained by my prof). A compiler for Opal was only available for Linux. I had zero experience with Linux and no intention to gain any. So I wrote my code without compliling/testing. Suprisingly, I got a good grade with a remark that the grade would have been even better without syntax errors :D
