fix test

IPython/html/tests/widgets/widget_button.js

@@ -39,7 +39,9 casper.notebook_test(function () {
     this.wait_for_output(button_index, 1);
 
     this.then(function () {
-        this.test.assertEquals(this.get_output_cell(button_index, 1).data['text/plain'], "'Clicked'",
+        this.test.assertEquals(this.get_output_cell(button_index, 1).text, "WARNING: The widget API is still considered experimental and \n    may change by the next major release of IPython.\n",
+            'Importing widgets show a warning');
+        this.test.assertEquals(this.get_output_cell(button_index, 2).data['text/plain'], "'Clicked'",
             'Button click event fires.');
     });
-});
  No newline at end of file
+});