gnome-base/gnome-settings-daemon requires dbusmock for test suite. In 3.22 this was optional, but will be hard required for tests in 3.24. We need to prepare for this in a timely manner as gnome-settings-daemon is a core component of GNOME and de-keywording would be rather disruptive.
However, if you want to avoid it, you can package.use.mask USE=test for gnome-settings-daemon instead and before unmasking the RESTRICT will be converted to RESTRICT="!test? ( test )" or such to avoid the dependency and restrict tests for your arch, while not running the tests, which would be unfortunate.
The gnome-settings-daemon still doesn't use dbusmock though, as some failures and such need still fixing, but dbusmock itself has a test suite itself as well for the keywording testing.
Gnome 3.24 is now in tree. If this is not swiftly keyworded, I'll have to start removing keywords. Thanks for your help. https://qa-reports.gentoo.org/output/gentoo-ci/aa4788643/output.html#gnome-base/gnome-settings-daemon
In the meantime, I pushed a package.use.mask, see commit a41e6d69673df0bbde7d7d648d0f7dce88877712.
I experienced a test failure (bug 627976) when I tried to keyword the package for x86. Please tell me if I should ignore the test failure for the moment and process with keywording.
~x86 added to >=dev-python/dbusmock-0.16.9.
I removed the package.use.mask for x86 as well.
~sparc keyworded (thanks to Rolf Eike Beer)