firestore/internal/conformance/testdata/update-st-alone.json

{
  "tests": [
    {
      "description": "update: ServerTimestamp alone",
      "comment": "If the only values in the input are ServerTimestamps, then no\nupdate mask should be produced in update operation.",
      "update": {
        "docRefPath": "projects/projectID/databases/(default)/documents/C/d",
        "jsonData": "{\"a\": \"ServerTimestamp\"}",
        "request": {
          "database": "projects/projectID/databases/(default)",
          "writes": [
            {
              "update": {
                "name": "projects/projectID/databases/(default)/documents/C/d"
              },
              "updateTransforms": [
                {
                  "fieldPath": "a",
                  "setToServerValue": "REQUEST_TIME"
                }
              ],
              "currentDocument": {
                "exists": true
              }
            }
          ]
        }
      }
    }
  ]
}