text: import pandas as pd
  import numpy as np
  import unittest
  
  class TestSeriesSub(unittest.TestCase):
      """
       Test the Pandas.Series.sub function
      
       sub() will subtract the elements of the corresponding indices from the Series it's called on and the Series passed as'other' argument.
       This tests focuses only on the parameters 'others',and the Series it's called on.
       The other parameters are not set and tested with their default values.
      """
      def setUp(self):
          # regular subtraction
          self.series1a = pd.Series([4,1,2,3])
          self.series1b = pd.Series([6,9,4,8])
          self.series1c = pd.Series([-2,-8,-2,-5])
          # subtraction with NaN
          self.series2a = pd.Series([1,np.nan,2,3])
          self.series2b = pd.Series([4,np.nan,np.nan,6])
          self.series2c = pd.Series([-3,np.nan,np.nan,-3])
          # subtraction with large series
          self.series3b = pd.Series(range(0,300000))
          self.series3a = pd.Series(range(0,600000,2))
          self.series3c = self.series3b
          # subtraction with empty series
          self.series4 = pd.Series([],dtype='int')
          # subtraction with different lengths
          self.series5a = pd.Series([2,4,5,6,8,9,10])
          self.series5b = self.series1b
          self.series5c = pd.Series([-4,-5,1,-2,np.nan,np.nan,np.nan])
          # Subtraction with indices
          self.series6a = pd.Series([6,1,2,3,4],["a","b","c","d","e"])
          self.series6b = pd.Series([5,6,7,1,8],["c","e","d","a","b"])
          self.series6c = pd.Series([5,-7,-3,-4,-2],["a","b","c","d","e"])
          # subtraction with indices and different lengths
          self.series7a = pd.Series([1,2,3,5],["f","g","a","b"])
          self.series7b = pd.Series([6,7,8,4,9,10],["c","d","e","f","g","h"])
          self.series7c = pd.Series([np.nan,np.nan,np.nan,np.nan,np.nan,-3,-7,np.nan],["a","b","c","d","e","f","g","h"])
      def test_series_sub_same_length(self):
          self.assertTrue(self.series1a.sub(self.series1b).equals(self.series1c))
          self.assertTrue(self.series2a.sub(self.series2b).equals(self.series2c))
          self.assertTrue(self.series3a.sub(self.series3b).equals(self.series3c))
          self.assertTrue(self.series4.sub(self.series4).equals(self.series4))
          self.assertTrue(self.series6a.sub(self.series6b).equals(self.series6c))
      def test_series_sub_different_length(self):
          self.assertTrue(self.series5a.sub(self.series5b).equals(self.series5c))
          self.assertTrue(self.series7a.sub(self.series7b).equals(self.series7c))
                          
  if __name__ == '__main__':
      unittest.main()                    
                          
                          
  
  
  
  
  
  