{
  "_comment": [
    "Inputs only. Expectations are measured -- see record.js.",
    "Pipeline-style updates: an update document that is an *array* of",
    "aggregation stages rather than a document of operators. The pinned crud",
    "corpus has five cases, one per command, and none of them is a refusal --",
    "so which stages are allowed, what happens to `_id`, and what an upsert",
    "does are all unmeasured there.",
    "Two shapes were authored and removed: an empty pipeline and an array",
    "holding a non-document. The driver rejects both before they reach a",
    "server ('Update document requires atomic operators'), so there is no",
    "server answer to record."
  ],
  "documents": [
    { "_id": 1, "x": 1, "y": 1, "t": { "u": { "v": 1 } } },
    { "_id": 2, "x": 2, "y": 1 }
  ],
  "cases": [
    {
      "description": "$replaceRoot keeps the _id it was given",
      "operation": "updateOne",
      "arguments": {
        "filter": { "_id": 1 },
        "update": [{ "$replaceRoot": { "newRoot": "$t" } }]
      }
    },
    {
      "description": "$replaceWith is the same stage under its short name",
      "operation": "updateOne",
      "arguments": { "filter": { "_id": 1 }, "update": [{ "$replaceWith": "$t" }] }
    },
    {
      "description": "$project keeps the _id it did not mention",
      "operation": "updateOne",
      "arguments": { "filter": { "_id": 1 }, "update": [{ "$project": { "x": 1 } }] }
    },
    {
      "description": "$project excluding _id keeps it anyway",
      "operation": "updateOne",
      "arguments": { "filter": { "_id": 1 }, "update": [{ "$project": { "_id": 0, "x": 1 } }] }
    },
    {
      "description": "$addFields adds to the document",
      "operation": "updateOne",
      "arguments": { "filter": { "_id": 1 }, "update": [{ "$addFields": { "foo": 1 } }] }
    },
    {
      "description": "$set is $addFields under its other name",
      "operation": "updateOne",
      "arguments": { "filter": { "_id": 1 }, "update": [{ "$set": { "foo": "$x" } }] }
    },
    {
      "description": "$unset of one field",
      "operation": "updateOne",
      "arguments": { "filter": { "_id": 1 }, "update": [{ "$unset": "y" }] }
    },
    {
      "description": "$unset of several fields",
      "operation": "updateOne",
      "arguments": { "filter": { "_id": 1 }, "update": [{ "$unset": ["y", "t"] }] }
    },
    {
      "description": "the stages run in order, each on the last one's output",
      "operation": "updateOne",
      "arguments": {
        "filter": { "_id": 1 },
        "update": [{ "$replaceRoot": { "newRoot": "$t" } }, { "$addFields": { "foo": 1 } }]
      }
    },
    {
      "description": "an expression reads the document the stage was handed",
      "operation": "updateOne",
      "arguments": {
        "filter": { "_id": 1 },
        "update": [{ "$addFields": { "z": { "$add": ["$x", "$y"] } } }]
      }
    },
    {
      "description": "a stage may restate the _id it already has",
      "operation": "updateOne",
      "arguments": { "filter": { "_id": 1 }, "update": [{ "$addFields": { "_id": 1 } }] }
    },
    {
      "description": "a stage may not change the _id",
      "operation": "updateOne",
      "arguments": { "filter": { "_id": 1 }, "update": [{ "$addFields": { "_id": 9 } }] }
    },
    {
      "description": "updateMany runs the pipeline on every match",
      "operation": "updateMany",
      "arguments": {
        "filter": {},
        "update": [{ "$project": { "x": 1 } }, { "$addFields": { "foo": 1 } }]
      }
    },
    {
      "description": "findOneAndUpdate with a pipeline",
      "operation": "findOneAndUpdate",
      "arguments": {
        "filter": { "_id": 1 },
        "update": [{ "$project": { "x": 1 } }, { "$addFields": { "foo": 1 } }],
        "returnDocument": "after"
      }
    },
    {
      "description": "an upsert runs the pipeline on the document the filter implies",
      "documents": [],
      "operation": "updateOne",
      "arguments": {
        "filter": { "k": 1 },
        "update": [{ "$addFields": { "a": 1 } }],
        "upsert": true
      }
    },
    {
      "description": "a pipeline that writes nothing new still reports a match",
      "operation": "updateOne",
      "arguments": { "filter": { "_id": 1 }, "update": [{ "$addFields": { "x": 1 } }] }
    },
    {
      "description": "$match is not allowed inside an update",
      "operation": "updateOne",
      "arguments": { "filter": { "_id": 1 }, "update": [{ "$match": { "x": 1 } }] }
    },
    {
      "description": "$group is not allowed inside an update",
      "operation": "updateOne",
      "arguments": { "filter": { "_id": 1 }, "update": [{ "$group": { "_id": null } }] }
    },
    {
      "description": "$sort is not allowed inside an update",
      "operation": "updateOne",
      "arguments": { "filter": { "_id": 1 }, "update": [{ "$sort": { "x": 1 } }] }
    },
    {
      "description": "$unwind is not allowed inside an update",
      "operation": "updateOne",
      "arguments": { "filter": { "_id": 1 }, "update": [{ "$unwind": "$t" }] }
    },
    {
      "description": "a stage name that is not a stage at all",
      "operation": "updateOne",
      "arguments": { "filter": { "_id": 1 }, "update": [{ "$bogus": {} }] }
    },
    {
      "description": "two stages packed into one array element",
      "operation": "updateOne",
      "arguments": {
        "filter": { "_id": 1 },
        "update": [{ "$addFields": { "a": 1 }, "$unset": "y" }]
      }
    },
    {
      "description": "arrayFilters alongside a pipeline",
      "operation": "updateOne",
      "arguments": {
        "filter": { "_id": 1 },
        "update": [{ "$addFields": { "a": 1 } }],
        "arrayFilters": [{ "i.b": 1 }]
      }
    }
  ]
}