What kind of test do you use?
Off the top of my head: pinching myself, checking small details, checking for internal consistency and/or odd gaps in recent memory (this one is the worst to know that my brain can fake), checking illumination levels, pretty much ANY variation of "you can't do X in a dream" (I can read, see color, and do comparison price shopping between competing brands with the price signs remaining consistent)
Light switches never work in my dream, but I always just assume the bulb burnt out and it drives me nuts that I can never use this as a reliable test. Maybe the dreams where the lights work are just not noteworthy enough to get remembered, though.
Well, I used to think that I do not believe in anything supernatural that affects what happens to me, but I'm wondering if maybe I actually do alieve in it. For example, a few days ago I had a close call in traffic, and when a collision I fully expected to happen just a second prior did not transpire, I mentally thanked... whom? I definitely had a clear feeling of gratitude for escaping, and I don't normally mean it literally when I say "Thank God!". So, who or what did I feel thankful to? I've never been religious, and I got rid of most of my superstitions over the years, but apparently there is still something there, and I do not know how to react to this knowledge.
What would be the proper reaction after a close call? Shrug and say "got lucky this time, should be more cautious next time"? What about when waiting for a diagnosis, what does sort-of-praying "please, please, let everything be OK" say about one's true beliefs? I know that I am much better at not blaming the world when something bad happens to me by chance than at not thanking the world when something good happens. Should it not be symmetric? Which part of a normally non-religious person wakes up and asserts itself in a crisis situation out of their control? Should it be embraced, suppressed, worked on?