old_contents: import unittest
  from .. import seq
  
  
  class TestStreams(unittest.TestCase):
      def test_open(self):
          with open('LICENSE.txt') as f:
              data = f.readlines()
          self.assertListEqual(data, seq.open('LICENSE.txt').to_list())
  
          text = ''.join(data).split(',')
          self.assertListEqual(text, seq.open('LICENSE.txt', delimiter=',').to_list())
  
new_contents: import unittest
  from .. import seq
  
  
  class TestStreams(unittest.TestCase):
      def test_open(self):
          with open('LICENSE.txt') as f:
              data = f.readlines()
          self.assertListEqual(data, seq.open('LICENSE.txt').to_list())
  
          text = ''.join(data).split(',')
          self.assertListEqual(text, seq.open('LICENSE.txt', delimiter=',').to_list())
  
          with self.assertRaises(ValueError):
              seq.open('LICENSE.txt', mode='w').to_list()
  
subject: add test case for not accepting write/append modes