Before downloading the test realm client patch, i would advise to delete EVERYTHING you have of modeledit material in your Wow folder, as theese will seriously mess up the installation of the new patch, and will lead to an incredibly ardous waste of time. I forgot to delete my model edits before i tried to install the teast realm client, wich resulted in a series of errors messages, corrupted files, and so on that were Wow related, and forced me to reinstall everything from patch 2.1 and forward ( blizz's repair unit luckily does all the deleting for you, atleast it did for me ). I presume this isnt anything new, but im merely trying to remind ppl to do this, since i wasted a hellufalot of time because i didnt myself.
Hope this will be usefull for some people
PS: The warning here is based solely on my own experience with the matter, since i don't know so much about how this system actually works and the technical reason for my troubles. Would be great if people that are more experienced with the nature of these issues then i am would comment constructively on this to clarify this and perhaps propose alternative methods for bypassing these problems.
PSPS: This knowledge alternatively also applies to the installation of the authentic 2.3 patch, though this is just presumed knowledge by myself, and should merely be regarded as measures of precaution