new_contents: from __future__ import absolute_import
  import matplotlib
  # Force matplotlib to not use any Xwindows backend.
  matplotlib.use('Agg')
  import matplotlib.pyplot as plt
  import datetime
  from matplotlib.dates import date2num
  import plotly.tools as tls
  from unittest import TestCase
  
  from plotly.tests.test_optional.optional_utils import compare_dict, run_fig
  
  
  class TestDateTimes(TestCase):
      def test_normal_mpl_dates(self):
          datetime_format = '%Y-%m-%d %H:%M:%S'
          y = [1, 2, 3, 4]
          date_strings = ['2010-01-04 00:00:00',
                          '2010-01-04 10:00:00',
                          '2010-01-04 23:00:59',
                          '2010-01-05 00:00:00']
  
          # 1. create datetimes from the strings
          dates = [datetime.datetime.strptime(date_string, datetime_format)
                   for date_string in date_strings]
  
          # 2. create the mpl_dates from these datetimes
          mpl_dates = date2num(dates)
  
          # make a figure in mpl
          fig, ax = plt.subplots()
          ax.plot_date(mpl_dates, y)
  
          # convert this figure to plotly's graph_objs
          pfig = tls.mpl_to_plotly(fig)
  
          print date_strings
          print pfig['data'][0]['x']
          # we use the same format here, so we expect equality here
          self.assertEqual(pfig['data'][0]['x'], date_strings)
  
subject: Add test for dates in mpl.