classes.java

@XStreamAlias("Race")
public class Race {
    @XStreamAlias("Name")
    public String name;
    @XStreamAlias("Drivers")
    @XStreamImplicit
    public List<Driver> drivers

     public Race() {
    	drivers = new ArrayList<Driver>();
    }
    public String toJson() {
    	XStream xstream = new XStream(new JsonHierarchicalStreamDriver());
		xstream.setMode(XStream.NO_REFERENCES);
		xstream.processAnnotations(Race.class);
		xstream.processAnnotations(Driver.class);
		String jsonString = xstream.toXML(this);
		return jsonString;
    }
}

@XStreamAlias("Driver")
public class Driver {
    public String name;
    public Integer number;
}

unitTest.java

import static org.junit.Assert.*;
import objects.Driver;
import objects.Race;

import org.junit.Test;



public class RaceTest {
	@Test
	public void testToJson() {
		
		String expectedJsonString = "{\"Race\": {\n" +
		"  \"Name\": \"Another Right Turn!\",\n" +
		"  \"Drivers\": [ {\n" +
		"    \"name\": \"JimBob\",\n" +
		"    \"number\": 3\n" +
		"  },\n" +
		"  {\n" +
		"    \"name\": \"BimJob\",\n" +
		"    \"number\": 13\n" +
		"  } ]\n" +
		"}}\n";
		
		String actualString;
		Race testRace = new Race();
		
		testRace.drivers.add(new Driver("JimBob", 3));
		testRace.drivers.add(new Driver("BimJob", 13));
		testRace.name = "Another Right Turn!";
		
		actualString = testRace.toJson();
		assertEquals(expectedJsonString,actualString);
	}
}