Add unit tests for RDocTask.
Add unit tests for RDocTask.

ruby/rake,taiganakagawa/rake,pjump/rake,pivotalforks/rake,mat/rake,envato/rake,jaustinhughey/rake,zzak/rake,ipmobiletech/rake,tmornini/rake,hsbt/rake,hsbt/rake,utilum/rake,bentley/rake,esasse/rake,envato/rake,pivotalforks/rake,askl56/rake,Vanzct/rake,88rabbit/rake,codedogfish/rake,mat/rake,ruby/rake