Coming from a background where I've only ever seen readings of a last will and testament in movies, what kind of style would be expected of such a document? Some personal stuff and then legalese generated from that, or something more elaborate?
In movies the structure is usually very straightforward, with "If something (optional), person X gets Y" style clauses. This is useful for the plot, but to me this seems to cover only the "last will" part of the document. So what constitutes the "testament" part? Are these even separable?
I am a lawyer from California and I can tell you there are very specific requirements to writing a valid Will. If you mess up (and people often do) the whole things winds up in Probate Court and costs a lot of money. And some people don't need a Will. They need a revocable living trust so that their estate can avoid a long and expensive probate court proceeding in the first place. But making this determination is one of the most important reasons that people should consult with an experienced estate planning attorney in their own area in the first place. To leave a lasting fulfilling legacy for your loved ones, don't rely on anything less.
As someone before said, it depends on the country you live in. Nevertheless, as far as I can tell after asking some lawyers I know (working in different countries), the common thing is try to make it as unambiguous as possible and get it notarized.
Testament and last will are, as far as "a document to legally state what you want to happen with your property when you die" gets, the same thing.