old_contents: import pytest
  
  from graphviz.base import Base
  
  
  def test_base_iter():
      base_inst = Base()
      with pytest.raises(NotImplementedError, match=r'subclasses'):
          iter(base_inst)
  
new_contents: import pytest
  
  from graphviz.base import Base
  
  
  @pytest.fixture(scope='module')
  def base():
      return Base()
  
  
  def test_base_iter_raises_notimplementederror(base):
      with pytest.raises(NotImplementedError, match=r'subclasses'):
          iter(base)
  
  
  def test_base_source_raises_notimplementederror(base):
      with pytest.raises(NotImplementedError, match=r'subclasses'):
          base.source
  
subject: increase test coverage