old_contents: import unittest
  import collections
  
  from pikos.filters.on_change import OnChange
  
  MockRecord = collections.namedtuple('MockRecord',['function', 'filename','line'])
  
  
  class TestOnValue(unittest.TestCase):
  
      def test_initialization(self):
  
          my_filter = OnChange('function')
          self.assertEqual(my_filter.field, 'function')
          self.assertIsNone(my_filter.previous)
  
      def test_call(self):
  
          my_filter = OnChange('filename')
          record = MockRecord('foo','bar.py', 3)
          self.assertTrue(my_filter(record))
          record = MockRecord('bar','foo.py', 7)
          self.assertTrue(my_filter(record))
          record = MockRecord('foo','foo.py', 123)
          self.assertFalse(my_filter(record))
  
  
  if __name__ == '__main__':
      unittest.main()
  
new_contents: import unittest
  import collections
  
  from pikos.filters.on_change import OnChange
  
  MockRecord = collections.namedtuple('MockRecord',['function', 'filename','line'])
  
  
  class TestOnChange(unittest.TestCase):
  
      def test_initialization(self):
  
          my_filter = OnChange('function')
          self.assertEqual(my_filter.field, 'function')
          self.assertIsNone(my_filter.previous)
  
      def test_call(self):
  
          my_filter = OnChange('filename')
          record = MockRecord('foo','bar.py', 3)
          self.assertTrue(my_filter(record))
          record = MockRecord('bar','foo.py', 7)
          self.assertTrue(my_filter(record))
          record = MockRecord('foo','foo.py', 123)
          self.assertFalse(my_filter(record))
  
  
  if __name__ == '__main__':
      unittest.main()
  
subject: correct testcase name