Speak to Menara Voidrender in the Barrens.
Hmm, you've made it this far... truly astonishing. I would have thought the corruption of channeling the arcane would have seeped into your very soul and driven you mad by now. How about we try and push you further then?
If you want to test your skill, seek out Menara Voidrender above Ratchet in Strahad's tower. She will guide you.