app-emulation/xen-3.0.2 fails src_test(), because the tests are for xend and the various xen utilities. With Gentoo splitting the upstream package into app-emulation/xen (hypervisor and headers) and app-emulation/xen-tools (xend, xm, python modules etc), app-emulation/xen needs RESTRICT="test".
Created attachment 92357 [details] log of FEATURES=test emerge xen
Fixed, thanks.