1.) There is no way to check for a null return value (at least, the documentation seems to imply this). I think this would be a useful addition -- would it be difficult to implement?
2.) Some of the advanced syntax of indextest.txt (i.e. how to call a method not activated in the properties file) is not documented -- it's probably worth adding it to http://code.google.com/p/solrmarc/wiki/Testing when time permits.
Let me know if I can be of any assistance in any of this (or if you think it's not worth bothering with)!
thanks,
Demian