How do you test a tweet?

Because I deal with a fair number of people who are new to social media marketing I'm often asked how you can test a Tweet? Usually by small charities frightened of what they think they "ought" to be doing.
Surely they say, the same message is broadcast to everyone?
Frankly, it is a bad idea to start tweeting straight away - a mistake I made - but if you wanted to you could try testing I suppose in the ways listed below, but appart from the first one - I would not recommend them. They are listed as ideas.
Firstly you can have topic related tweet accounts - you don't have to use one account. There are tools that help you mangae more than one account and importantly have more than one person accessing the same account (ie for Customer Service)
Secondly, surely if you need to say something you have to test you should consider using tiny urls - good tweeting use these anyway to measure impact and to link off to snippets of interest. In which case a Tweet is less of a broadcast and the first X clicks can see something different to the next X. I'd worry about doing this if your intention is duplicitous, if your merely testing what works and what does not it might work.
You can't use Tiny URLs to hide from the public record as there are plenty of ways to snapshot or print screen and if the public thought you were being duplicitous you'd be in real trouble. But perhaps it would be OK for standard marketing testing of different approaches and how people react as long as the level of testing is tweeking (appearance etc) not wholescale revision.
There is nothing to stop you having a testing panel that you pre-tweet to through a unique account or even via a different media.
And finally, if you are uncertain what the reaction will be... don't.
My biggest worry about brands that ask these questions is are they trying to be something they are not. There is a tendancy to naively think you "must be cool" to use Twitter and for cool read "edgy"... the truth is you have to deliver what you stand for. Be true to yourself or you'll be another dancing dad.