如何使用robolectric测试应用程序类中的方法？

我刚刚开始使用Robolectric，并设法按照此处的说明进行操作：

http://robolectric.org/eclipse-quick-start

来运行样本。

我要测试的第一件事是应用程序类中的方法，但是尝试运行它时出现以下错误。我在下面的代码中进行强制转换的是哪一行。

我想我不是要获取我的应用程序实例的正确方法。用Robolectric获取应用程序类的实例的正确方法是什么？

java.lang.ClassCastException: android.app.Application cannot be cast to com.gmail.npnster.first_project.MyApp
    at com.gmail.npnster.first_project.MyAppTest.setUp(MyAppTest.java:32)
    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:483)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:24)
    at org.robolectric.RobolectricTestRunner$2.evaluate(RobolectricTestRunner.java:250)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
    at org.robolectric.RobolectricTestRunner$1.evaluate(RobolectricTestRunner.java:177)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

这是我的测试课：

@RunWith(RobolectricTestRunner.class)
public class MyAppTest  {

    private 

    MyApp app ;
    @Before
    public void setUp() throws Exception {
        // TODO Auto-generated method stub

        app = (MyApp) Robolectric.application;
        app.clearToken();
        app.clearEmailId();
    }


    @Test
    public void testInitalToken() {
        assertThat(app.getToken(), equalTo(""));

    }

    @Test
    public void testSaveToken() {
        String testToken = "test_token";
        app.saveToken(testToken);
        assertThat(app.getToken(), equalTo(testToken));

    }

}