firestore/internal/conformance/testdata/update-prefix-2.json

{
  "tests": [
    {
      "description": "update: prefix #2",
      "comment": "In the input data, one field cannot be a prefix of another.",
      "update": {
        "docRefPath": "projects/projectID/databases/(default)/documents/C/d",
        "jsonData": "{\"a\": 1, \"a.b\": 2}",
        "isError": true
      }
    }
  ]
}