For SLE 15 SP1 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:jayvdb:py-backports/SLE_15_SP1/home:jayvdb:py-backports.repo
zypper refresh
zypper install python3-mock
For SLE 15 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:jayvdb:py-backports/SLE_15/home:jayvdb:py-backports.repo
zypper refresh
zypper install python3-mock
For SLE 12 SP4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:jayvdb:py-backports/SLE_12_SP4/home:jayvdb:py-backports.repo
zypper refresh
zypper install python3-mock