Added a text cell in the notebook to test run_nb.

IPython/core/tests/test_run.py

@@ -377,6 +377,7 b' tclass.py: deleting object: C-third'
         nb = current.new_notebook(
             worksheets=[
                 current.new_worksheet(cells=[
+                    current.new_text_cell("The Ultimate Question of Everything"),
                     current.new_code_cell("answer=42")
                 ])
             ]