Q:

Triggering Canon Speedlite manually

I was planning to take a fake multiple-exposure picture: use a dark room, long exposure time, and manually trigger a flash for each exposure. But can I trigger my Canon Speedlite 430EX II manually without any extra gear?
This would be trivial if I had two camera bodies, but no such luck.
Of course there is the test button in the Speedlite unit. But exactly what does the test button do? How much flash power do I get this way; can it be adjusted by using the manual mode? Is it just a tiny burst of light so that I can see that the unit is alive, or can I use the test button to get consistent exposures?

A:

Your test button should firing at whatever power you select manually.  I can't speak to that specific model, but it has on a few different flash brands I've tried.  
Its pretty easy to tell if it does.  

Just set it to high, take a picture and press the test button.  
Set it to low, take a picture and press the test button.  Is there a big difference? Probably so.

You should get consistent exposures with it.
If for some crazy it doesn't, you can always electrically tape a couple of wires to the bottom pin and plate and just short the connection together with a momentary push button ( or just touching the wires together)- that's what the camera does.

