How do I unit test my action's validation logic

public class WebLoginActionTest extends TestCase {
    
    private WebLoginAction wla;
    
    protected void setUp() throws Exception {
        wla = new WebLoginAction();
        wla.setJ_username("");
        wla.setJ_password(null);
        super.setUp();
    }
 
    public void testWebLoginActionValidation() throws ValidationException {
        ActionValidatorManager avm = ActionValidatorManagerFactory.getInstance();        
        
        avm.validate(wla,"");
        Map fieldErrors = wla.getFieldErrors();
        
        assertTrue(wla.hasErrors());
        assertEquals(2, fieldErrors.size());
        assertTrue(fieldErrors.containsKey("j_username"));
        assertTrue(fieldErrors.containsKey("j_password"));
                
        System.out.println("[errors] : " +  fieldErrors.toString());              
    }
}