firestore/internal/conformance/testdata/update-badchar.json

{
  "tests": [
    {
      "description": "update: invalid character",
      "comment": "The keys of the data given to Update are interpreted, unlike those of Create and Set. They cannot contain special characters.",
      "update": {
        "docRefPath": "projects/projectID/databases/(default)/documents/C/d",
        "jsonData": "{\"a~b\": 1}",
        "isError": true
      }
    }
  ]
}