diff --git a/t/clipper.t b/t/clipper.t
index 59051f156..7d316dde9 100644
--- a/t/clipper.t
+++ b/t/clipper.t
@@ -2,52 +2,72 @@ use Test::More;
 use strict;
 use warnings;
 
-plan tests => 1;
+plan tests => 3;
 
 use Math::Clipper ':all';
 
-my $clipper = Math::Clipper->new;
 
-my $square = [ # ccw
-    [10, 10],
-    [20, 10],
-    [20, 20],
-    [10, 20],
-];
-
-my $hole_in_square = [  # cw
-    [14, 14],
-    [14, 16],
-    [16, 16],
-    [16, 14],
-];
-
-my $square2 = [  # ccw
-    [5, 12],
-    [25, 12],
-    [25, 18],
-    [5, 18],
-];
-
-$clipper->add_subject_polygons([ $square, $hole_in_square ]);
-$clipper->add_clip_polygons([ $square2 ]);
-my $intersection = $clipper->ex_execute(CT_INTERSECTION, PFT_NONZERO, PFT_NONZERO);
-
-is_deeply $intersection, [
-    {
-        holes => [
-            [
-                [14, 16],
-                [16, 16],
-                [16, 14],
-                [14, 14],
+{
+    my $square = [ # ccw
+        [10, 10],
+        [20, 10],
+        [20, 20],
+        [10, 20],
+    ];
+    my $hole_in_square = [  # cw
+        [14, 14],
+        [14, 16],
+        [16, 16],
+        [16, 14],
+    ];
+    my $square2 = [  # ccw
+        [5, 12],
+        [25, 12],
+        [25, 18],
+        [5, 18],
+    ];
+    my $clipper = Math::Clipper->new;
+    $clipper->add_subject_polygons([ $square, $hole_in_square ]);
+    $clipper->add_clip_polygons([ $square2 ]);
+    my $intersection = $clipper->ex_execute(CT_INTERSECTION, PFT_NONZERO, PFT_NONZERO);
+    is_deeply $intersection, [
+        {
+            holes => [
+                [
+                    [14, 16],
+                    [16, 16],
+                    [16, 14],
+                    [14, 14],
+                ],
             ],
-        ],
-        outer => [
-            [10, 18],
-            [10, 12],
-            [20, 12],
-            [20, 18],
-        ],
-    },
-], 'hole is preserved after intersection';
+            outer => [
+                [10, 18],
+                [10, 12],
+                [20, 12],
+                [20, 18],
+            ],
+        },
+    ], 'hole is preserved after intersection';
+}
+
+#==========================================================
+
+{
+    my $contour1 = [ [0,0],   [40,0],  [40,40], [0,40]  ];  # ccw
+    my $contour2 = [ [10,10], [30,10], [30,30], [10,30] ];  # ccw
+    my $hole     = [ [15,15], [15,25], [25,25], [25,15] ];  # cw
+    
+    my $clipper = Math::Clipper->new;
+    $clipper->add_subject_polygons([ $contour1, $contour2, $hole ]);
+    my $union = $clipper->ex_execute(CT_UNION, PFT_NONZERO, PFT_NONZERO);
+    is_deeply $union, [{ holes => [], outer => [ [0,40], [0,0], [40,0], [40,40] ] }],
+        'union of two ccw and one cw is a contour with no holes';
+    
+    $clipper->clear;
+    $clipper->add_subject_polygons([ $contour1, $contour2 ]);
+    $clipper->add_clip_polygons([ $hole ]);
+    my $diff = $clipper->ex_execute(CT_DIFFERENCE, PFT_NONZERO, PFT_NONZERO);
+    is_deeply $diff, [{ holes => [[ [15,25], [25,25], [25,15], [15,15] ]], outer => [ [0,40], [0,0], [40,0], [40,40] ] }],
+        'difference of a cw from two ccw is a contour with one hole';
+}
+