方法setUp＆＃34; not mocked＆＃34;尝试在Android下测试按钮时出错

Question

我试图编写一个Android单元测试，测试是否在MainActivity中按下ImageButton会触发启动另一个活动的意图（Activity2）。这是我的代码：

public class MainActivityTest extends ActivityUnitTestCase<MainActivity> {
    private Intent activityLaunchIntent;

    public MainActivityTest(){
        super(MainActivity.class);
    }

    @Override
    protected void setUp() throws Exception {
        super.setUp();
        activityLaunchIntent = new Intent(getInstrumentation().getTargetContext(), MainActivity.class);
    }

    public void testPreconditions() {
        assertNotNull(activityLaunchIntent);
    }

    /**
     * Tests that the button to launch Activity2 fires the correct Intent.
     */
    @MediumTest
    public void testLaunchButton_shouldLaunchActivity2() {
        startActivity(activityLaunchIntent, null, null);
        final ImageButton launchActivity2Button = (ImageButton) getActivity().findViewById(R.id.launchButton);
        launchButton.performClick();

        // Ensure that the intent to start the Activity2 has been launched 
        final Intent launchActivity2Intent = getStartedActivityIntent();
        assertNotNull(launchActivity2Intent);
        assertTrue(launchActivity2Intent.getClass().equals(SettingsActivity.class));
        assertTrue(isFinishCalled());
    }
}

当我尝试从AndroidStudio中运行单元测试时，我收到以下错误：

java.lang.RuntimeException: Method setUp in android.test.ActivityUnitTestCase not mocked. See http://g.co/androidstudio/not-mocked for details.
    at android.test.ActivityUnitTestCase.setUp(ActivityUnitTestCase.java)

访问http://g.co/androidstudio/not-mocked后，我将以下内容添加到build.gradle文件中：

android {
  // ...
  testOptions { 
    unitTests.returnDefaultValues = true
  }
}

但是，现在我收到以下错误：

java.lang.NullPointerException
    at com.example.unittesting.MainActivityTest.setUp(MainActivityTest.java:24)

顺便提一下，MainActivityTest.java的第24行是：

activityLaunchIntent = new Intent(getInstrumentation().getTargetContext(), MainActivity.class);

有人可以告诉我这里发生了什么吗？这是一个简单的修复吗？或者我是以完全错误的方式做这件事。提前感谢您的帮助。