In Mormon Doctrine, a testimony is explained as follows:
A testimony of the gospel “is received when the Holy Spirit speaks to the spirit within [us]; it comes when the whisperings of the still small voice are heard.
So I think the answer is yes, you can. I believe that the Holy Spirit will absolutely speak truths to us regarding the Adversary, but after a week of study, I realized how short-sighted the question was. I don't think that I would be recognizing the whisperings of a still, small voice regarding Satan, if I didn't already have a testimony of the Savior. As I become more aware of the temptations and snares of Satan in my life, I can easily trace that awareness back to truth or wisdom for which he is attempting to distract.
I believe that testimony of doctrine is constantly growing and being shaped. I believe that testimony requires awareness, work, and vigilance on our part so that it becomes ever stronger. I believe that the Holy Spirit will speak to us and confirm things of all nature...even Satan...if it will help us to grow and understand the Father and the Son on a more intimate level.