i think a couple of bitcoin exchanges had a demo account that you could use with something like 1000BTC in it to test things. go check out Kraken i think they had that.

but in my opinion you don't really need fake/demo account in crypto trading world. the minimum amount required to trade is very small. for example many sites have a minimum of 0.0001-0.0005BTC and that is less than a dollar.
things here are nothing like Forex or Stocks market. you can start with a tiny amount of money and learn things that way.
and remember with real money you gain real experience.