{
  "tests": [
    {
      "description": "update: non-letter starting chars are quoted, except underscore",
      "comment": "In a field path, any component beginning with a non-letter or underscore is quoted.",
      "update": {
        "docRefPath": "projects/projectID/databases/(default)/documents/C/d",
        "jsonData": "{\"_0.1.+2\": 1}",
        "request": {
          "database": "projects/projectID/databases/(default)",
          "writes": [
            {
              "update": {
                "name": "projects/projectID/databases/(default)/documents/C/d",
                "fields": {
                  "_0": {
                    "mapValue": {
                      "fields": {
                        "1": {
                          "mapValue": {
                            "fields": {
                              "+2": {
                                "integerValue": "1"
                              }
                            }
                          }
                        }
                      }
                    }
                  }
                }
              },
              "updateMask": {
                "fieldPaths": [
                  "_0.`1`.`+2`"
                ]
              },
              "currentDocument": {
                "exists": true
              }
            }
          ]
        }
      }
    }
  ]
}