Test GenericWritable using MRUnit

Question

Say for example, I have a class like below :

public class MyGenericWritable extends GenericWritable {

    private static Class<? extends Writable>[] CLASSES = null;

    static {
        CLASSES = (Class<? extends Writable>[]) new Class[] {
            FirstClass.class,
            SecondClass.class
             //add as many different class as you want
        };
    }
    //this empty initialize is required by Hadoop
    public MyGenericWritable() {
    }

    public MyGenericWritable(Writable instance) {
        set(instance);
    }

    @Override
    protected Class<? extends Writable>[] getTypes() {
        return CLASSES;
    }

    @Override
    public String toString() {
        return "MyGenericWritable [getTypes()=" + Arrays.toString(getTypes()) + "]";
    }
}

here is the mapper :

public static class FirstMap extends Mapper<Text, FirstClass, Text, MyGenericWritable> {
     public void map(Text key, FirstClass value, Context context) throws IOException, InterruptedException {
         System.out.println("FirstMap:" + key.toString() + " " + value.toString());
         context.write(key, new MyGenericWritable(value));
     }
}

Is there a way to test mapper using MapDriver in MRUnit ? Note : The reason I ask is because using .withOutput will not validate the results

Or should I use .run() method and assert the results manually ?