{
  "expression": [
    "boolean",
    ["in", ["get", "substr"], ["string", ["get", "str"]]]
  ],
  "inputs": [
    [{}, {"properties": {"substr": null, "str": "helloworld"}}],
    [{}, {"properties": {"substr": "foo", "str": "helloworld"}}],
    [{}, {"properties": {"substr": "low", "str": "helloworld"}}],
    [{}, {"properties": {"substr": "low", "str": null}}]
  ],
  "expected": {
    "compiled": {
      "result": "success",
      "isFeatureConstant": false,
      "isZoomConstant": true,
      "type": "boolean"
    },
    "outputs": [
      false,
      false,
      true,
      {"error":"Expected value to be of type string, but found null instead."}
    ],
    "serialized": [
      "boolean",
      ["in", ["get", "substr"], ["string", ["get", "str"]]]
    ]
  }
}