old_contents: class Vertex:
      def __init__(self):
          self.adj = []  # A list of vertices this vertex points to
  
      def add_adjacent(self, other_vertex):
          self.adj.add(other_vertex)
  
      def remove_adjacent(self, other_vertex):
          self.adj.remove(other_vertex)
  
      def adjacences(self):
          return self.adj
  
  class Bug(Vertex):
      pass
  
  class Chunk(Vertex):
  
      def __init__(self):
          super(Vertex, self).__init__()
          self.tested = False
  
      def is_tested(self):
          return self.tested
  
      def set_tested(self, tested):
          self.tested = tested
  
  
new_contents: class Vertex:
      def __init__(self):
          self.adj = []  # A list of vertices this vertex points to
  
      def add_adjacent(self, other_vertex):
          self.adj.add(other_vertex)
  
      def remove_adjacent(self, other_vertex):
          self.adj.remove(other_vertex)
  
      def adjacences(self):
          return self.adj
  
  '''
      The chunks a bug affects are its adjacent vertices
      i.e. if a bug applies to a chunk, add the chunk as an adjacent vertex
  '''
  class Bug(Vertex):
      pass
  
  '''
      The bugs a chunk's tests will detect are the adjacent vertices
      i.e. if a chunk detects a bug, add the bug as an adjacent vertex
  '''
  class Chunk(Vertex):
  
      def __init__(self):
          Vertex.__init__(self)
          self.tested = False
          self.detects = []
  
      def is_tested(self):
          return self.tested
  
      def set_tested(self, tested):
          self.tested = tested
subject: Change to environment