Unit testing JSON Swift

I am working on an iOS application written in Swift which parse a lot of JSON files. The JSON structures are sophisticated and I would to test them before to map JSON to object.

For example test if the key 'users' exists and for each user the structure('name', 'first', 'last').

{
  "users": [
    {
      "name": {
        "first": "emmi",
        "last": "wiita"
      }
    },
    {
      "name": {
        "first": "erdi",
        "last": "nielen"
      }
    },
    {
      "name": {
        "first": "daniel",
        "last": "beck"
      }
    }
 ]
}

Are there any good way to do this?

Thanks.