I can reproduce by running 'debuild binary' inside the build directory. I've modified testsuite/gdk/display.c to redirect stdout/stderr to a file and I get:
(/home/bob/bzr/ubuntu/build-area/gtk+3.0-3.12.2/debian/build/shared/testsuite/gdk/.libs/lt-display:18477): Gdk-ERROR **: error: XDG_RUNTIME_DIR not set in the environment.
So something is going wrong in the environment. Note I do have XDG_RUNTIME_DIR set in my environment.
I can reproduce by running 'debuild binary' inside the build directory. I've modified testsuite/ gdk/display. c to redirect stdout/stderr to a file and I get:
(/home/ bob/bzr/ ubuntu/ build-area/ gtk+3.0- 3.12.2/ debian/ build/shared/ testsuite/ gdk/.libs/ lt-display: 18477): Gdk-ERROR **: error: XDG_RUNTIME_DIR not set in the environment.
So something is going wrong in the environment. Note I do have XDG_RUNTIME_DIR set in my environment.