用StrutsTestCase测试struts Action时,报空指针异常?

//设置了action-config.xml
  <action path="/user"
  type="web.org.exblog.webapp.action.UserAction">
  <forward name="success" path="/index.jsp" />
  </action>
 
 
  public class UserActionTest extends MockStrutsTestCase {
 
  public void testExecute() {
 
  setRequestPathInfo("user");
  addRequestParameter("id", "1");
  actionPerform(); // 报错信息指定为这一行.错误信息见下:
  verifyForward("success");
  verifyNoActionErrors();
  }
  }
 
 
  错误信息:
  (struts.MockStrutsTestCase 330 ) Error initializing action servlet
  javax.servlet.ServletException
  at org.apache.struts.action.ActionServlet.initServlet(ActionServlet.java:1437)
  at org.apache.struts.action.ActionServlet.init(ActionServlet.java:466)
  at javax.servlet.GenericServlet.init(GenericServlet.java:211)
  at servletunit.struts.MockStrutsTestCase.getActionServlet(MockStrutsTestCase.java:326)
  at servletunit.struts.MockStrutsTestCase.actionPerform(MockStrutsTestCase.java:394)
  at web.org.exblog.action.UserActionTest.testExecute(UserActionTest.java:14)
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
  There was 1 error:
  1) testExecute(web.org.exblog.action.UserActionTest)java.lang.NullPointerException
  at servletunit.struts.MockStrutsTestCase.getActionServlet(MockStrutsTestCase.java:331)
  at servletunit.struts.MockStrutsTestCase.tearDown(MockStrutsTestCase.java:130)
  at web.org.exblog.action.UserActionTest.main(UserActionTest.java:20)
 
  14行为:actionPerform();
报空指针异常
------解决方法--------------------------------------------------------
没建ActionForm吧？