Add spec to test that when duplicate users are added to group
Add spec to test that when duplicate users are added to group

harryggg/coursemology2,BenMQ/coursemology2,BenMQ/coursemology2,Coursemology/coursemology2,xzhflying/coursemology2,xzhflying/coursemology2,cysjonathan/coursemology2,Coursemology/coursemology2,Coursemology/coursemology2,harryggg/coursemology2,Coursemology/coursemology2,cysjonathan/coursemology2,cysjonathan/coursemology2,BenMQ/coursemology2,Coursemology/coursemology2,Coursemology/coursemology2,harryggg/coursemology2,xzhflying/coursemology2,Coursemology/coursemology2