add test for single `cannot` definition
add test for single `cannot` definition

dgynn/cancancan,antonifs/cancan,chadzilla2080/cancan,ReaxDev/cancancan,chenxin0723/cancancan,sideci-sample/sideci-sample-cancan,travis-repos/cancan,mccraigmccraig/cancan,jackquack/cancan,docount/cancan,xbits/cancan,GeorgeZhukov/cancancan,mattbrictson/cancan,hunterae/cancan,dima4p/cancancan,CanCanCommunity/cancancan,macmartine/cancancan-ruby,adamliesko/cancancan,jhawthorn/cancancan,uversity/cancan,mv288/cancan,0612800232/cancan,nerde/cancancan,neomadara/cancancan,tiarly/cancancan,gdpelican/cancancan,NelsonScott/cancancan,roaaangel/cancancan,StartupWeekend/cancan,chadzilla2080/cancancan,ryanb/cancan,coorasse/cancancan,moss-zc/cancan,VoroninNick/cancan,phallguy/cancancan,greenriver/cancan,Ahnita/cancancan,MetricMike/cancancan