For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/devel:libraries:libyui/openSUSE_Tumbleweed/devel:libraries:libyui.repo
zypper refresh
zypper install rubygem-libyui-rake
For openSUSE Factory run the following as root:
zypper addrepo https://download.opensuse.org/repositories/devel:libraries:libyui/openSUSE_Factory/devel:libraries:libyui.repo
zypper refresh
zypper install rubygem-libyui-rake
For assis repo checker run the following as root:
zypper addrepo https://download.opensuse.org/repositories/devel:libraries:libyui/assis_repo_checker/devel:libraries:libyui.repo
zypper refresh
zypper install rubygem-libyui-rake
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/devel:libraries:libyui/15.6/devel:libraries:libyui.repo
zypper refresh
zypper install rubygem-libyui-rake