firestore/internal/conformance/testdata/update-paths-arrayunion-noarray.json

{
  "tests": [
    {
      "description": "update-paths: ArrayUnion cannot be in an array value",
      "comment": "ArrayUnion must be the value of a field. Firestore\ntransforms don't support array indexing.",
      "updatePaths": {
        "docRefPath": "projects/projectID/databases/(default)/documents/C/d",
        "fieldPaths": [
          {
            "field": [
              "a"
            ]
          }
        ],
        "jsonValues": [
          "[1, 2, [\"ArrayRemove\", 1, 2, 3]]"
        ],
        "isError": true
      }
    }
  ]
}