code: def test_next_data(self):
      # Check that next will correctly return the next available
      # line and plays well with the dunder_iter part.
      mock = mock_open(read_data="foo\nbar\nbaz\n")
      with patch("%s.open" % __name__, mock, create=True):
          h = open("bar")
          line1 = next(h)
          line2 = next(h)
          lines = [l for l in h]
      self.assertEqual(line1, "foo\n")
      self.assertEqual(line2, "bar\n")
      self.assertEqual(lines[0], "baz\n")
      self.assertEqual(h.readline(), "")
  
imports: import unittest
  from warnings import catch_warnings
  from test.test_unittest.testmock.support import is_instance
  from unittest.mock import MagicMock, Mock, patch, sentinel, mock_open, call
label_desc: Use image node_id 8 for calling the TestMockOpen obj's underlying member method code with example usage: obj.test_next_data() without return types