old_contents: import pyfakefs
  import pytest
  
  from mutil import commands
  
  
  @pytest.fixture
  def playlist(fs):
      """Open a fake file object
      Args:
          fs: A reference to the `pyfakefs` filesystem
      """
      fs.CreateFile('playlist')
      with open('playlist', 'r+') as playlist:
          yield playlist
  
  
  @pytest.mark.parametrize('test_input, expectation, duplicates_expected', [
      ('a/b/c\na/b/c\n1/2/3', 'a/b/c\n1/2/3', 1),  # Duplicated
      ('a/b/c\n1/2/3', 'a/b/c\n1/2/3', 0),         # Non-duplicated
      ('', '', 0),                                 # Empty
  ])
  def test_remove_playlist_duplicates(playlist, test_input, expectation, duplicates_expected):
      playlist.write(test_input)
      playlist.seek(0)
  
      duplicates_found = commands.remove_playlist_duplicates(playlist)
      reality = playlist.read()
  
      assert duplicates_expected == duplicates_found
      assert expectation == reality
  
  
  class TestPlaylistPathCommands:
      library_path = '/home/$USER/Music/'
      library_path_w_trailing_slash = library_path + '/'
      absolute_path = '/home/$USER/Music/album/track'
      relative_path = 'album/track'
  
      @pytest.mark.parametrize('test_input, expectation', [
          (absolute_path, relative_path),  # Absolute to relative
          (relative_path, relative_path)   # Relative to relative
      ])
      @pytest.mark.parametrize('library_path', [(library_path), (library_path_w_trailing_slash)])
      def test_playlist_paths_use_relative(self, playlist, test_input, expectation, library_path):
          playlist.write(test_input)
          playlist.seek(0)
  
          commands.playlist_paths_use_relative(playlist, library_path)
  
          reality = playlist.read()
          assert expectation == reality
  
      @pytest.mark.parametrize('test_input, expectation', [
          (relative_path, absolute_path),  # Relative to absolute
          (absolute_path, absolute_path)   # Absolute to absolute
      ])
      def test_playlist_paths_use_absolute(self, playlist, test_input, expectation):
          playlist.write(test_input)
          playlist.seek(0)
  
          commands.playlist_paths_use_absolute(playlist, self.library_path)
  
          reality = playlist.read()
          assert expectation == reality
  
new_contents: import pyfakefs
  import pytest
  
  from mutil import commands
  
  
  @pytest.fixture
  def playlist(fs):
      """Open a fake file object
      Args:
          fs: A reference to the `pyfakefs` filesystem
      """
      fs.CreateFile('playlist')
      with open('playlist', 'r+') as playlist:
          yield playlist
  
  
  @pytest.mark.parametrize('test_input, expectation, duplicates_expected', [
      ('a/b/c\na/b/c\n1/2/3', 'a/b/c\n1/2/3', 1),  # Duplicated
      ('a/b/c\n1/2/3', 'a/b/c\n1/2/3', 0),         # Non-duplicated
      ('', '', 0),                                 # Empty
  ])
  def test_remove_playlist_duplicates(playlist, test_input, expectation, duplicates_expected):
      playlist.write(test_input)
      playlist.seek(0)
  
      duplicates_found = commands.remove_playlist_duplicates(playlist)
      reality = playlist.read()
  
      assert duplicates_expected == duplicates_found
      assert expectation == reality
  
  
  class TestPlaylistPathCommands:
      library_path = '/home/$USER/Music/'
      library_path_w_trailing_slash = library_path + '/'
      absolute_path = '/home/$USER/Music/album/track'
      relative_path = 'album/track'
  
      @pytest.mark.parametrize('test_input, expectation', [
          (absolute_path, relative_path),  # Absolute to relative
          (relative_path, relative_path)   # Relative to relative
      ])
      @pytest.mark.parametrize('library_path', [library_path, library_path_w_trailing_slash])
      def test_playlist_paths_use_relative(self, playlist, test_input, expectation, library_path):
          playlist.write(test_input)
          playlist.seek(0)
  
          commands.playlist_paths_use_relative(playlist, library_path)
  
          reality = playlist.read()
          assert expectation == reality
  
      @pytest.mark.parametrize('test_input, expectation', [
          (relative_path, absolute_path),  # Relative to absolute
          (absolute_path, absolute_path)   # Absolute to absolute
      ])
      def test_playlist_paths_use_absolute(self, playlist, test_input, expectation):
          playlist.write(test_input)
          playlist.seek(0)
  
          commands.playlist_paths_use_absolute(playlist, self.library_path)
  
          reality = playlist.read()
          assert expectation == reality
  
subject: Remove some redundant parenthesises