added tests for utils' mergeObjects()

+(function(t) {
+    t.comment('mergeObjects()');
+
+    var testCases = [
+        {
+            obj1: {a: 1}, obj2: {b: 2}, merged: {a: 1, b: 2}
+        },
+        {
+            obj1: {}, obj2: {a: 1}, merged: {a: 1}
+        },
+        {
+            obj1: {a: 1}, obj2: {}, merged: {a: 1}
+        },
+        {
+            obj1: {a: 1}, obj2: {a: 2}, merged: {a: 2}
+        },
+        {
+            obj1:   {x: 0, double: function(){return this.x*2;}},
+            obj2:   {triple: function(){return this.x*3;}},
+            merged: {
+                x: 0,
+                double: function(){return this.x*2;},
+                triple: function(){return this.x*3;}
+            }
+        }
+    ];
+
+    testCases.forEach(function(testCase) {
+        t.assertEquals(mergeObjects(testCase.obj1, testCase.obj2), testCase.merged, 'mergeObjects() can merge objects');
+    });
+
+    t.done();
+})(casper.test);