test(dropdown): reorganize and refactor tests
test(dropdown): reorganize and refactor tests

Closes #4896

wesleycho/bootstrap,wesleycho/bootstrap,caoruiy/bootstrap,caoruiy/bootstrap,RobJacobs/bootstrap,shootermv/bootstrap,Servoy/bootstrap,benhalverson/bootstrap,mabi/bootstrap,justin-john/bootstrap-1,infowrap/bootstrap,BookingBug/bootstrap,shiftagent/ui-bootstrap,fpipita/bootstrap,burlhock/bootstrap,Servoy/bootstrap,292388900/bootstrap,Kpler/bootstrap,connyay/bootstrap,icfantv/bootstrap,looker/bootstrap,BookingBug/bootstrap,Lincoln-xzc/angular-ui-bootstrap,icfantv/bootstrap,byronigoe/bootstrap,deeg/bootstrap,vfiles/bootstrap,Foxandxss/bootstrap,christor/bootstrap,benhalverson/bootstrap,justin-john/bootstrap-1,benhalverson/bootstrap,christor/bootstrap,benhalverson/bootstrap,deeg/bootstrap,RobJacobs/bootstrap,shiftagent/ui-bootstrap,connyay/bootstrap,angular-ui/bootstrap,matteopic/bootstrap,Lincoln-xzc/angular-ui-bootstrap,matteopic/bootstrap,mabi/bootstrap,292388900/bootstrap,vfiles/bootstrap,shootermv/bootstrap,byronigoe/bootstrap,infowrap/bootstrap,Kpler/bootstrap,angular-ui/bootstrap,Foxandxss/bootstrap,fpipita/bootstrap,looker/bootstrap,burlhock/bootstrap