in openSUSE Tumbleweed, there are currently two ruby versions avaialble (and
most rubygems exist in both versions)

YaST does not specify for its rubygems if it wants them for ruby2.1 or ruby2.2,
which can lead the solver to mix and match the rubygems.

A sample openQA test case tripping over this is:

https://openqa.opensuse.org/tests/125360

The ruby packages installed on the machine are:
>ruby-2.2-3.4.x86_64
>ruby-common-2.1-9.1.noarch
>ruby2.1-2.1.8-2.10.x86_64
>ruby2.1-rubygem-abstract_method-1.2.1-3.2.x86_64
>ruby2.1-rubygem-cfa-0.3.0-2.1.x86_64
>ruby2.1-rubygem-cheetah-0.4.0-2.1.x86_64
>ruby2.1-rubygem-fast_gettext-0.9.2-5.2.x86_64
>ruby2.1-rubygem-gem2rpm-0.10.1-3.7.x86_64
>ruby2.1-rubygem-ruby-augeas-0.5.0-2.2.x86_64
>ruby2.1-rubygem-ruby-dbus-0.9.3-3.2.x86_64
>ruby2.1-stdlib-2.1.8-2.10.x86_64
>ruby2.2-2.2.4-2.10.x86_64
>ruby2.2-rubygem-fast_gettext-1.0.0-3.3.x86_64
>ruby2.2-rubygem-gem2rpm-0.10.1-9.12.x86_64
>ruby2.2-rubygem-ruby-dbus-0.11.0-6.8.x86_64
>ruby2.2-stdlib-2.2.4-2.10.x86_64

Dependencies on RPM / solver level are satisfied. /usr/bin/ruby is ruby2.2

The best way is for yast to change it's requires from unspecified versions like

> rubygem(abstract_method) => meaning, ANY rubygem, 2.1 or 2.2 based
to
> rubygem(%rb_default_ruby_abi:abstract_method) => meaning, Distribution default ruby based rubygem