firestore/internal/conformance/testdata/update-del-nested.json

{
  "tests": [
    {
      "description": "update: Delete cannot be nested",
      "comment": "The Delete sentinel must be the value of a top-level key.",
      "update": {
        "docRefPath": "projects/projectID/databases/(default)/documents/C/d",
        "jsonData": "{\"a\": {\"b\": \"Delete\"}}",
        "isError": true
      }
    }
  ]
}