When creating a Copr project, one can specify which chroots, i.e. which distribution version and architecture combinations, to enable. Examples of chroots are fedora-27-x86_64, epel-7-ppc64le, fedora-rawhide-i386 etc.

However, there is no easy to use option to enable testing repositories, e.g. the updates-testing repository for Fedora Branched and stable releases, when specifying the chroots. Let me show you how you can easily achieve that by specifying an extra repository with a parameterized URL.