fix unicode literal in v4.test_convert

caused failure on Python 2 on Windows

because unicode!

IPython/nbformat/v4/tests/test_convert.py

@@ -1,72 +1,72
 # -*- coding: utf-8 -*-
 import copy
 
 import nose.tools as nt
 
 from IPython.nbformat import validate
 from .. import convert
 
 from . import nbexamples
 from IPython.nbformat.v3.tests import nbexamples as v3examples
 from IPython.nbformat import v3, v4
 
 def test_upgrade_notebook():
     nb03 = copy.deepcopy(v3examples.nb0)
     validate(nb03)
     nb04 = convert.upgrade(nb03)
     validate(nb04)
 
 def test_downgrade_notebook():
     nb04 = copy.deepcopy(nbexamples.nb0)
     validate(nb04)
     nb03 = convert.downgrade(nb04)
     validate(nb03)
 
 def test_upgrade_heading():
     v3h = v3.new_heading_cell
     v4m = v4.new_markdown_cell
     for v3cell, expected in [
         (
             v3h(source='foo', level=1),
             v4m(source='# foo'),
         ),
         (
             v3h(source='foo\nbar\nmulti-line\n', level=4),
             v4m(source='#### foo bar multi-line'),
         ),
         (
-            v3h(source='ünìcö∂e–cønvërsioñ', level=4),
+            v3h(source=u'ünìcö∂e–cønvërsioñ', level=4),
             v4m(source=u'#### ünìcö∂e–cønvërsioñ'),
         ),
     ]:
         upgraded = convert.upgrade_cell(v3cell)
         nt.assert_equal(upgraded, expected)
 
 def test_downgrade_heading():
     v3h = v3.new_heading_cell
     v4m = v4.new_markdown_cell
     v3m = lambda source: v3.new_text_cell('markdown', source)
     for v4cell, expected in [
         (
             v4m(source='# foo'),
             v3h(source='foo', level=1),
         ),
         (
             v4m(source='#foo'),
             v3h(source='foo', level=1),
         ),
         (
             v4m(source='#\tfoo'),
             v3h(source='foo', level=1),
         ),
         (
             v4m(source='# \t  foo'),
             v3h(source='foo', level=1),
         ),
         (
             v4m(source='# foo\nbar'),
             v3m(source='# foo\nbar'),
         ),
     ]:
         downgraded = convert.downgrade_cell(v4cell)
         nt.assert_equal(downgraded, expected)