1) Goto Content->Products
2) Select Repo Discovery
3) paste https://fedorapeople.org/groups/katello/releases/yum/nightly/ as repo to discover
4) Select a couple of repos
5) Create Selected
6) In the create product page, use an existing product but clear the name of repo and hit submit.
Notice you get an error that looks like
{"name":["can't be blank","cannot be blank"]}
Instead  of a nicer "Name cannot be blank" form message.