It's funny that the working reality tests for dreaming are pretty stupid and decidedly non-philosophical. For instance, the virtual reality the brain sets up for dreams apparently isn't good enough to do text or numbers properly, so when you are dreaming you're unable to read the same text twice and see it saying the same thing, and digital clocks never work right. (There's an interesting parallel here to the fact that written language is a pretty new thing in evolutionary scale and people probably don't have that much evolved cognitive capacity to deal with it.)

There's a whole bunch of these: http://en.wikibooks.org/wiki/Lucid_Dreaming/Induction_Techniques#Reality_checks