new_contents: #!/usr/bin/python
  
  """
     Copyright 2013 nilmtk authors.
  
     Licensed under the Apache License, Version 2.0 (the "License");
     you may not use this file except in compliance with the License.
     You may obtain a copy of the License at
  
         http://www.apache.org/licenses/LICENSE-2.0
  
     Unless required by applicable law or agreed to in writing, software
     distributed under the License is distributed on an "AS IS" BASIS,
     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     See the License for the specific language governing permissions and
     limitations under the License.
  """
  
  from __future__ import print_function, division
  import unittest
  import nilmtk.stats.electricity.single as single
  import numpy as np
  import pandas as pd
  
  class TestSingle(unittest.TestCase):
      def test_tz_to_naive(self):
          START = '2010/1/1'
          F = 'D' # frequency
          P = 48 # periods
          dti_naive = pd.date_range(START, freq=F, periods=P)
  
          def test_dti(tz):
              dti = pd.date_range(START, freq=F, periods=P, tz=tz)
              dti_calc = single._tz_to_naive(dti)
              for ts_calc, ts_naive in zip(dti_calc, dti_naive):
                  self.assertEqual(ts_calc, ts_naive)
  
          tzs = ['US/Eastern', 'UTC', 'WET', 'CET', 'Asia/Kolkata']
          for tz in tzs:
              test_dti(tz)
  
  if __name__ == '__main__':
      unittest.main()
  
subject: Add test for _tz_to_naive()