I just tried to spike something, and as usual, I created a console app and started hacking.
It is a non trivial spike, so I started refactoring it to allow proper separation and actually let me handle the complexity that I am trying to contain.
I couldn't continue the spike. Literally. I had no idea how to go about it.
I am currently in the process of moving the spike code into a proper environment, one that has tests, so I can actually work in small increment, and not try to implement the whole thing in a single go.
About an hour later, I have this mostly complete and working, and I can see how the tests helped me get into a situation where I can actually make a small set of changes are get things working.