{
  "_comment": [
    "Inputs only. Expectations are measured -- see record.js.",
    "`$addToSet`, `$pop` and `$pullAll`: the three array operators that are",
    "neither `$push` nor `$pull`. Each has a shape that decides whether it",
    "wrote at all -- a set that already held the value, a pop of an empty",
    "array, a pullAll matching nothing -- and `modifiedCount` is the only",
    "place that shows, which is why every case records an outcome too."
  ],
  "documents": [{ "_id": 1, "t": [1, 2, 3] }],
  "cases": [
    {
      "description": "$addToSet appends a value the array does not hold",
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$addToSet": { "t": 4 } } }
    },
    {
      "description": "$addToSet on a value already there writes nothing",
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$addToSet": { "t": 2 } } }
    },
    {
      "description": "$addToSet on a missing field creates the array",
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$addToSet": { "gone": 1 } } }
    },
    {
      "description": "$addToSet $each adds only what is missing",
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$addToSet": { "t": { "$each": [2, 4, 5] } } } }
    },
    {
      "description": "$addToSet $each with duplicates inside it",
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$addToSet": { "t": { "$each": [7, 7] } } } }
    },
    {
      "description": "$addToSet compares documents whole",
      "documents": [{ "_id": 1, "t": [{ "a": 1 }] }],
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$addToSet": { "t": { "a": 1 } } } }
    },
    {
      "description": "$addToSet distinguishes documents by field order",
      "documents": [{ "_id": 1, "t": [{ "a": 1, "b": 2 }] }],
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$addToSet": { "t": { "b": 2, "a": 1 } } } }
    },
    {
      "description": "$addToSet treats an int and an equal double as one value",
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$addToSet": { "t": 2.0 } } }
    },
    {
      "description": "$addToSet on a non-array field",
      "documents": [{ "_id": 1, "t": 5 }],
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$addToSet": { "t": 1 } } }
    },
    {
      "description": "$pop removes the last element",
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$pop": { "t": 1 } } }
    },
    {
      "description": "$pop with -1 removes the first",
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$pop": { "t": -1 } } }
    },
    {
      "description": "$pop of an empty array writes nothing",
      "documents": [{ "_id": 1, "t": [] }],
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$pop": { "t": 1 } } }
    },
    {
      "description": "$pop of a missing field writes nothing",
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$pop": { "gone": 1 } } }
    },
    {
      "description": "$pop of a one-element array leaves an empty one",
      "documents": [{ "_id": 1, "t": [9] }],
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$pop": { "t": 1 } } }
    },
    {
      "description": "$pop with an argument that is neither 1 nor -1",
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$pop": { "t": 2 } } }
    },
    {
      "description": "$pop with 1.0, which is 1",
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$pop": { "t": 1.0 } } }
    },
    {
      "description": "$pop of a non-array field",
      "documents": [{ "_id": 1, "t": 5 }],
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$pop": { "t": 1 } } }
    },
    {
      "description": "$pullAll removes every copy of every listed value",
      "documents": [{ "_id": 1, "t": [1, 2, 3, 2] }],
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$pullAll": { "t": [2] } } }
    },
    {
      "description": "$pullAll with several values",
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$pullAll": { "t": [1, 3] } } }
    },
    {
      "description": "$pullAll matching nothing writes nothing",
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$pullAll": { "t": [9] } } }
    },
    {
      "description": "$pullAll compares documents whole, not by predicate",
      "documents": [{ "_id": 1, "t": [{ "a": 1 }, { "a": 2 }] }],
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$pullAll": { "t": [{ "a": 1 }] } } }
    },
    {
      "description": "$pullAll on a missing field writes nothing",
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$pullAll": { "gone": [1] } } }
    },
    {
      "description": "$pullAll with an argument that is not an array",
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$pullAll": { "t": 1 } } }
    },
    {
      "description": "$pullAll emptying the array",
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$pullAll": { "t": [1, 2, 3] } } }
    },
    {
      "description": "$addToSet through a positional segment",
      "documents": [{ "_id": 1, "y": [{ "t": [1] }, { "t": [2] }] }],
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$addToSet": { "y.$[].t": 1 } } }
    },
    {
      "description": "$pop down a dotted path",
      "documents": [{ "_id": 1, "n": { "t": [1, 2] } }],
      "operation": "updateOne",
      "arguments": { "filter": {}, "update": { "$pop": { "n.t": -1 } } }
    }
  ]
}