Add a test to demonstrate errors when up/down arrow keys are

pressed in an empty notebook.

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

@@ -0,0 +1,31
+//
+// Check for errors with up and down arrow presses in an empty notebook.
+//
+casper.openNewNotebook();
+
+casper.then(function () {
+    var result = this.evaluate(function() {
+        var ncells = IPython.notebook.ncells(),
+            i;
+        
+        // Delete all cells.
+        for (i = 0; i < ncells; i++) {
+            IPython.notebook.delete_cell();
+        }
+        
+        // Simulate the "up arrow" and "down arrow" keys.
+        var up_press = jQuery.Event("keydown", {which: 38});
+        $(document).trigger(up_press);
+        var down_press = jQuery.Event("keydown", {which: 40});
+        $(document).trigger(down_press);
+        return true;
+    });
+    casper.test.assertTrue(result, 'Trivial assertion to check for JS errors');
+});
+
+casper.deleteCurrentNotebook();
+
+// Run the browser automation.
+casper.run(function() {
+    this.test.done();
+});