testsuite: Add opacity handling test for fill nodes

testsuite/gsk/compare/fill-opacity.node

@@ -0,0 +1,26 @@
+opacity {
+  child: fill {
+    child: opacity {
+      opacity: 0.4;
+      child: color {
+        bounds: 0 0 50 50;
+        color: rgb(0,255,0);
+      }
+    }
+    path: "\
+M 10 0\
+L 40 0\
+L 40 10\
+L 50 10\
+L 50 40\
+L 40 40\
+L 40 50\
+L 10 50\
+L 10 40\
+L 0 40\
+L 0 10\
+L 10 10\
+Z";
+    fill-rule: winding;
+  }
+}

testsuite/gsk/meson.build

@@ -66,6 +66,7 @@ compare_render_tests = [
   'empty-texture',
   'empty-transform',
   'fill',
+  'fill-opacity',
   'fill-with-3d-contents-nogl-nocairo',
   'huge-height',
   'huge-width',