[
  {
    "id": "$replaceRoot example",
    "stage": "$replaceRoot",
    "kind": "example",
    "pipeline": [
      {
        "$replaceRoot": {
          "newRoot": "$address"
        }
      }
    ],
    "input": [
      {
        "name": "Alice",
        "address": {
          "city": "Toronto"
        }
      }
    ],
    "result": [
      {
        "city": "Toronto"
      }
    ]
  },
  {
    "id": "$replaceRoot empty input",
    "stage": "$replaceRoot",
    "kind": "empty input",
    "pipeline": [
      {
        "$replaceRoot": {
          "newRoot": "$address"
        }
      }
    ],
    "input": [],
    "result": []
  },
  {
    "id": "$replaceRoot invalid specification",
    "stage": "$replaceRoot",
    "kind": "invalid specification",
    "pipeline": [
      {
        "$replaceRoot": null
      }
    ],
    "input": [
      {
        "name": "Alice",
        "address": {
          "city": "Toronto"
        }
      }
    ],
    "error": "IllegalArgumentException",
    "message": "$replaceRoot requires 'newRoot' field"
  },
  {
    "id": "$replaceRoot missing root",
    "stage": "$replaceRoot",
    "kind": "missing root",
    "pipeline": [
      {
        "$replaceRoot": {
          "newRoot": "$address"
        }
      }
    ],
    "input": [
      {}
    ],
    "error": "IllegalArgumentException",
    "message": "$replaceRoot evaluated to non-object: null"
  }
]