Generally* you can't,
*however functions without Arduino specific calls may be testable in a standard C++ environment e.g. Visual Studio 2008. But as ints, floats, doubles, RAM etc may have other sizes, this creates its own pitfalls. ==> don't do it
Is it something that could be done, I mean in future releases of the Arduino IDE, or is it simply impossible to do due to some technical stuff in the compiler?
Regards Thomas