BitMEX have lunched some time ago a platform which you can trade BTC in a test environment at real time market prices.
They load you up with 0.1BTC and you can test strategies without loosing any money.
That's so cool! finally a platform that lets you do those things,
Next step I call exchanges to do testnet for a REST API, BTW if some platform does have testnet for API trading please let me know in the comments :)
It's unreal testing code with real money heh.
you can join BitMEX testnet here: https://testnet.bitmex.com/register/oLgcN0
Have FUN! that's the best way to gain confidence and just try out !