new JsonDeserializer(); The type or namespace name jsonDeserializer could not be found (Are you missing a using directive or an assembly reference?)

    [TestMethod]
    public void TestMethod1()
    {
        var client = new RestClient("http://localhost:3000");
        var request=new RestRequest("posts/{postid}", Method.Get);
        request.AddUrlSegment("postid", 1);
        var response= client.Execute(request);
        var deserialize = new JsonDeserializer();  
        var output= deserialize.Deserialize<Dictionary<string, string>>(response);

        var result = output["author"];


        Assert.That(result, Is.EqualTo("Karthik K"), "Author is not correct");


    }
}

}

Getting error for below two lines:

1. var deserialize = new JsonDeserializer(); //Error CS0246 The type or namespace name 'type/namespace' could not be found (are you missing a using directive or an assembly reference?)

2. var result = output["author"]; // Error CS0021 Cannot apply indexing with [] to an expression of type 'type'

Note: I am using Community edition which is free