Navré is part of the Milkymist System-on-Chip, the most advanced open source SoC for interactive multimedia applications.
Even though simple C programs can be run, the Navré softcore still contains several bugs and testers are most welcome.
The idea is to use Verilog simulations to run and verify every instruction just like the simulavr test suite (which can be used for inspiration). Simple and incomplete test benches can be found with the SoftUSB core.
If you are interested in carrying out this work because you need an AVR compatible softcore in your design or just as a contribution to the Milkymist project, please contact the Milkymist-devel mailing list or drop by the #milkymist channel on the FreeNode IRC network.
I will happily fix any bug you may find!