Yours should look something like this G:\Electronic Arts\Ultima Online Classic\client.exe
You want to choose the drive it is on and then work your way to the folder it is installed in and then eventually to the client.exe
Test Center is a shard and you choose it like you would any other production shard.
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As you can see here I dropped a stack of blood moss into my bag and uoassist is registering it on my screen so it does work with the new patch on test center.
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If you have any questions, I can try and walk you through getting it set up.