[
  {
    "input": {"books": [0, 1, 2, 3]},
    "output": 2,
    "states": [
      "PassState"
    ]
  },

  {
    "input": {"books": [0]},
    "error": {
      "Error": "DefaultStateError",
      "Cause": "No Matches!"
    },
    "states": [
      "FirstState", "ChoiceState", "DefaultState"
    ]
  }
]