anchor.diff:    GraphState copyWith({
       GraphData graphData,
       GraphCurrentState graphCurrentState,
  +    GraphType graphType,
       String yAxis,
       Failure failure,
       String failureMessage,
  
positive.code:   GraphState({
      @required this.graphData,
      @required this.graphCurrentState,
      @required this.yAxis,
      this.failure,
      this.failureMessage,
  
negative.code:   success,
  }
  
  enum GraphType {
    playsByDate,
    playsByDayOfWeek,
    playsByHourOfDay,
  }
  
  class GraphState extends Equatable {
    final GraphData graphData;
    final GraphCurrentState graphCurrentState;
    final GraphType graphType;
    final String yAxis;
    final Failure failure;
    final String failureMessage;
  