{
  "expression": ["length", ["string", ["get", "x"]]],
  "inputs": [[{}, {"properties": {"x": "a string"}}]],
  "expected": {
    "compiled": {
      "result": "success",
      "isFeatureConstant": false,
      "isZoomConstant": true,
      "type": "number"
    },
    "outputs": [8],
    "serialized": ["length", ["string", ["get", "x"]]]
  }
}