The ebuild states: # Bug #270851: test needs TCL support if use tcl || use test ; then myconf+=( --enable-tcl --with-tcl=/usr/$(get_libdir) ) else myconf+=(--disable-tcl ) fi With no extra helper code, this means that with FEATURES=test USE=-tcl, all tcl stuff gets built and installed, obviously without proper RDEPEND. What is more funny, the tests aren't run anyway due to bug #425106.
Solved w/ REQUIRED_USE