I've had fun practicing on http://www.codewars.com/ http://www.codewars.com/ You can choose your languages and it's all wrapped in a nice leveling-up game styl

I've had fun practicing on http://www.codewars.com/ http://www.codewars.com/ You can choose your languages and it's all wrapped in a nice leveling-up game style. You pass and rank up based on your solutions to predefined community problems, and have a test-driven approach enforced in the editor.