old_contents: import pytest
  from emcee_functools import Fixed
  
  
  def test_fixed_can_contain_a_value():
      f = Fixed(5)
      assert f.value == 5
  
  
  def test_fixed_value_does_not_change():
      f = Fixed(5)
      with pytest.raises(ValueError) as err:
          f.value += 5
  
  
  def test_fixed_value_does_not_change_at_class_level():
      f = Fixed(5)
      with pytest.raises(ValueError) as err:
          f += 5
  
  
  def test_string_representation():
      f = Fixed(5)
      assert str(f) == '<Fixed value 5>'
  
new_contents: import pytest
  from emcee_functools import Fixed
  
  
  @pytest.fixture
  def fixed():
      return Fixed(5)
  
  
  def test_fixed_can_contain_a_value(fixed):
      assert fixed.value == 5
  
  
  def test_fixed_value_does_not_change(fixed):
      with pytest.raises(ValueError) as err:
          fixed.value += 5
  
  
  def test_fixed_value_does_not_change_at_class_level(fixed):
      with pytest.raises(ValueError) as err:
          fixed += 5
  
  
  def test_string_representation(fixed):
      assert str(fixed) == '<Fixed value 5>'
  
subject: add Fixed(5) fixture