Add CasperJS tests for `merge_cell_above()` and `merge_cell_below()`.

IPython/frontend/html/notebook/tests/casperjs/test_cases/merge_cells.js

@@ -0,0 +1,37 b''
+//
+// Test merging two notebook cells.
+//
+casper.notebookTest(function() {
+    var output = this.evaluate(function () {
+        // Fill in test data.
+        var set_cell_text = function () {
+            var cell_one = IPython.notebook.get_selected_cell();
+            cell_one.set_text('a = 5');
+            
+            IPython.notebook.insert_cell_below('code');
+            var cell_two = IPython.notebook.get_selected_cell();
+            cell_two.set_text('print a');
+        };
+        
+        // merge_cell_above()
+        set_cell_text();
+        IPython.notebook.merge_cell_above();
+        var merged_above = IPython.notebook.get_selected_cell();
+        
+        // merge_cell_below()
+        set_cell_text();
+        IPython.notebook.select(0);
+        IPython.notebook.merge_cell_below();
+        var merged_below = IPython.notebook.get_selected_cell();
+        
+        return {
+            above: merged_above.get_text(),
+            below: merged_below.get_text()
+        };
+    });
+    
+    this.test.assertEquals(output.above, 'a = 5\nprint a',
+                           'Successful insert_cell_above().');
+    this.test.assertEquals(output.below, 'a = 5\nprint a',
+                           'Successful insert_cell_below().');
+});