[
  {
    "id": "$facet example",
    "stage": "$facet",
    "kind": "example",
    "pipeline": [
      {
        "$facet": {
          "first": [
            {
              "$limit": 1
            }
          ],
          "names": [
            {
              "$project": {
                "name": 1
              }
            }
          ]
        }
      }
    ],
    "input": [
      {
        "name": "A"
      },
      {
        "name": "B"
      }
    ],
    "result": [
      {
        "first": [
          {
            "name": "A"
          }
        ],
        "names": [
          {
            "name": "A"
          },
          {
            "name": "B"
          }
        ]
      }
    ]
  },
  {
    "id": "$facet empty input",
    "stage": "$facet",
    "kind": "empty input",
    "pipeline": [
      {
        "$facet": {
          "first": [
            {
              "$limit": 1
            }
          ],
          "names": [
            {
              "$project": {
                "name": 1
              }
            }
          ]
        }
      }
    ],
    "input": [],
    "result": [
      {
        "first": [],
        "names": []
      }
    ]
  },
  {
    "id": "$facet invalid specification",
    "stage": "$facet",
    "kind": "invalid specification",
    "pipeline": [
      {
        "$facet": null
      }
    ],
    "input": [
      {
        "name": "A"
      },
      {
        "name": "B"
      }
    ],
    "error": "IllegalArgumentException",
    "message": "$facet stage requires an object as its argument"
  }
]