add get_rendered_contents helper function

notebook/tests/selenium/test_markdown.py

@@ -13,6 +13,15 @@ def notebook(authenticated_browser):
     return Notebook.new_notebook(authenticated_browser)
 
 
+def get_rendered_contents(nb):
+    cl = ["text_cell", "render"]
+    rendered_cells = [cell.find_element_by_class_name("text_cell_render") 
+                      for cell in nb.cells 
+                      if all([c in cell.get_attribute("class") for c in cl])]
+    return [x.get_attribute('innerHTML').strip()
+            for x in rendered_cells 
+            if x is not None]
+
 def test_markdown_cell(notebook):
     nb = notebook
     nb[:] = ["# Foo"]