In Debian builds, we run the test suite under Xvfb as the build daemons don't have X running. This used to work fine, but 3.21.x has introduced a regression that causes a SIGFPE in gdkscreen-x11.c:

Program received signal SIGFPE, Arithmetic exception.
0x00007ffff3be3168 in init_randr15 (screen=0x628000, changed=0x7fffffffe614) at /build/gtk+3.0-3.21.4/./gdk/x11/gdkscreen-x11.c:477
477	                  refresh_rate = (1000 * xmode->dotClock) / (xmode->hTotal *xmode->vTotal);
(gdb) p *xmode
$1 = {id = 68, width = 640, height = 480, dotClock = 0, hSyncStart = 0, hSyncEnd = 0, hTotal = 0, hSkew = 0, vSyncStart = 0, vSyncEnd = 0, 
  vTotal = 0, name = 0x622140 "640x480", nameLength = 7, modeFlags = 0}


root@tatooine:/tmp/buildd/gtk+3.0-3.21.4/debian/build/shared/testsuite/gdk# xvfb-run xrandr --verbose
xrandr: Failed to get size of gamma for output screen
Screen 0: minimum 1 x 1, current 640 x 480, maximum 640 x 480
screen connected 640x480+0+0 (0x44) normal (normal) 0mm x 0mm
	Identifier: 0x46
	Timestamp:  545194463
	Subpixel:   unknown
	Clones:    
	CRTC:       0
	CRTCs:      0
	Transform:  1.000000 0.000000 0.000000
	            0.000000 1.000000 0.000000
	            0.000000 0.000000 1.000000
	           filter: 
  640x480 (0x44)  0.000MHz *current
        h: width   640 start    0 end    0 total    0 skew    0 clock   0.00KHz
        v: height  480 start    0 end    0 total    0           clock   0.00Hz