So, you want to help us testing tomb: great.
How can you do it? It depends on 1) what you want to test 2) what _distro_ you use / how skilled are you
In tomb sources extras/test the directory contains test units for Tomb.
Run make to go through all test units, this will try various operations with tomb and return a list of success or failures.
The devs are writing some new feature, and you want to help them testing it. In this situation, there is not a stable release you can refer to. Instead, you'll have to refer to the git user/branch which has the code you want to test. It could be in the "main" branch (that is: user=dyne, branch=master) or in a specific branch of some user (example: user=boyska, branch=optparsing)
The AUR contains tomb-git package. You can install it with yaourt -S tomb-git, and it will install the "main" development branch (user=dyne, branch=master). If you want to use a specific branch, you can just edit the PKGBUILD in the lines that say
#You can customize _gituser and _gitbranch to test specific developer's repo _gituser="dyne" _gitbranch="master"
_gitbranchaccording to your needs.
Now, you can test tomb!