Retrofit Polymophism Test

SimpleRetrofitTest.java

import com.fasterxml.jackson.annotation.JsonProperty;
import okhttp3.OkHttpClient;
import org.junit.jupiter.api.Test;
import retrofit2.Call;
import retrofit2.Retrofit;
import retrofit2.converter.jackson.JacksonConverterFactory;
import retrofit2.http.Body;
import retrofit2.http.POST;

import java.io.IOException;

public class SimpleRetrofitTest {
    public static interface Vehicle {
    }

    public static class Car implements Vehicle {
        @JsonProperty("type")
        public String type() {  return "car"; }
    }

    public static class Lorry implements Vehicle {
        @JsonProperty("type")
        private String type() {  return "car"; }
        @JsonProperty("cargo")
        private String cargo() {  return "toys"; }
    }

    public interface Service {
        @POST("/api/")
        public Call<String> upload(@Body Car vehicle);
    }

    @Test
    public void test() throws IOException {
        final OkHttpClient client = new OkHttpClient();
        //client.interceptors().add(new FakeInterceptor());
        var retrofit = new Retrofit.Builder()
                .addConverterFactory(JacksonConverterFactory.create())
                .baseUrl("http://whatever/") //We fail before we hit this!
                .client(client)
                .build();

        Service service = retrofit.create(Service.class);
        var call = service.upload(new Car());
        call.execute();

    }
}