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I can't see any issues, as you only want to install a test site parallel. Search the forums for more answers, you are not the first to post this question.
What you need to do though, when installing your test system, is to ensure that the second XOOPS installation uses a different prefix for the database tables, that is all! You can set this during installation time (I believe it is the second page during install proecedure).
Hope this helps.