Tests are restricted because "Test causes a circular depend on gtk+... since gtk+ needs cairo but test needs gtk+ so we need to block it". That doesn't seem like a very good reason. We have other instances of recursive dependencies in portage. Now, the test suite fails.. but that's another matter.
The test suite for cairo is incredibly fragile; even upstream's README basically says that they don't expect 100% of the tests to pass: > It's generally been very difficult to achieve a test run with zero > failures. The difficulties stem from the various versions of the many > libraries that the test suite depends on, (it depends on a lot more > than cairo itself), as well as fonts and other system-specific > settings. If your system differs significantly from the system on > which the reference images were generated, then you will likely see > the test suite reporting "failures", (even if cairo is working just > fine). So I don't think it's a good idea to enable such a test suite with FEATURES=test. Maybe hide it behind USE=regression-test like gcc does?
Upstream test suite fails all over the place. Doesn't seem like something we should allow users to hit via portage.
