I don't know if you have to by law, but it is certainly something I would do before selling (or even giving them away). Electrical contractors can do it and apply a certifying sticker. My son was in hospital recently and I purchased a brand new dvd player from a retail store for him, and the hospital still insisted on my having it tested and certified before he could use it. I took it to a guy who tested it and certified it (for free when I told him what it was for) so I can't say what it costs normally, but the cosequences of something going wrong are too serious to contemplate.
Even charity stores have to have their gear certified before sale.
Hope this helps,
Marina.
