java.lang.NullPointerException at org.apache.struts2.StrutsTestCase.getActionProxy

使用junit测试structs的action时出现
java.lang.NullPointerException
at org.apache.struts2.StrutsTestCase.getActionProxy

代码：

package action;

import dao.UserDao;
import org.apache.struts2.StrutsSpringTestCase;
import org.apache.struts2.StrutsTestCase;
import org.easymock.EasyMock;
import org.junit.Before;
import org.junit.Test;

import com.opensymphony.xwork2.ActionProxy;
import service.UserService;

import java.util.HashMap;
import java.util.Map;

import static org.easymock.EasyMock.replay;

public class LoginActionTest extends StrutsSpringTestCase  {

    // 重写父类方法,指定配置文件的名字
    protected String[] getContextLocations() {
        return new String[] { "struts.xml", "applicationContext.xml" };
    }

    private UserService userService;

    @Before
    public void setUp() throws Exception{
        userService = EasyMock.createMock(UserService.class);
    }


    @Test
    public void testExecute() throws Exception {

        ActionProxy proxy = getActionProxy("/loginAction");
        LoginAction test = (LoginAction) proxy.getAction();
        assertNotNull(test);

        test.setUsername("u1");
        test.setPassword("1");
        Map session=new HashMap();
        test.setSession(session);
        test.setUserService(userService);
        EasyMock.expect(userService.loginVerify("u1","1")).andReturn(true);
        replay(userService);
        String result = proxy.execute();
        assertEquals("success", result);
    }
}

报错：

java.lang.NullPointerException
	at org.apache.struts2.StrutsTestCase.getActionProxy(StrutsTestCase.java:131)
	at action.LoginActionTest.testExecute(LoginActionTest.java:37)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at junit.framework.TestCase.runTest(TestCase.java:176)
	at junit.framework.TestCase.runBare(TestCase.java:141)
	at junit.framework.TestResult$1.protect(TestResult.java:122)
	at junit.framework.TestResult.runProtected(TestResult.java:142)
	at junit.framework.TestResult.run(TestResult.java:125)
	at junit.framework.TestCase.run(TestCase.java:129)
	at junit.framework.TestSuite.runTest(TestSuite.java:252)
	at junit.framework.TestSuite.run(TestSuite.java:247)
	at org.junit.internal.runners.JUnit38ClassRunner.run(JUnit38ClassRunner.java:86)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
	at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:220)
	at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:53)

原因是我覆盖了继承的StrutsSpringTestCase的setUp函数
需要加上super.setUp()才能正确

    @Before
    public void setUp() throws Exception{
        super.setUp();
        userService = EasyMock.createMock(UserService.class);
    }