facebook screenshot-tests-for-android thow NullPointer on make screenshot

Question

In my test

@LargeTest
@RunWith(AndroidJUnit4.class)
public class SimpleActicityTest {


@Rule
public ActivityTestRule<MainActivity> activityActivityTestRule =
        new ActivityTestRule<>(MainActivity.class);

@Test
public void testActivity() throws Exception {
    Activity a = activityActivityTestRule.getActivity();
    Screenshot.snapActivity(activity).setName("s1").record();
}

I have

ava.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.app.Instrumentation.getContext()' on a null object reference
at com.facebook.testing.screenshot.internal.ScreenshotImpl.getInstance(ScreenshotImpl.java:338)
at com.facebook.testing.screenshot.Screenshot.snapActivity(Screenshot.java:45)
at com.mobium.reference.activity.Util.takeScreenshot(Util.java:32)
at com.mobium.reference.activity.SimpleActicityTest.lambda$testLeftMenuTest$1(SimpleActicityTest.java:52)
at com.mobium.reference.activity.SimpleActicityTest.access$lambda$0(SimpleActicityTest.java)
at com.mobium.reference.activity.SimpleActicityTest$$Lambda$1.run(Unknown Source)
at android.os.Handler.handleCallback(Handler.java:815)
at android.os.Handler.dispatchMessage(Handler.java:104)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5549)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:964)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:759)

source of faceebook's lib getInstance():

public static ScreenshotImpl getInstance() {
        if(sInstance != null) {
            return sInstance;
        } else {
            Class var0 = ScreenshotImpl.class;
            synchronized(ScreenshotImpl.class) {
                if(sInstance != null) {
                    return sInstance;
                } else {
                    Instrumentation instrumentation = Registry.getRegistry().instrumentation;
                    Bundle arguments = Registry.getRegistry().arguments;
                    HostFileSender hostFileSender = new HostFileSender(instrumentation, arguments);
                    sInstance = create(instrumentation.getContext(), arguments, hostFileSender);
                    return sInstance;
                }
            }
        }
    }

It creates Registry and take public field instrumentation, but there are not instrumentation initializations in Registry constructor. How it can work?

Answer 1

If you want to use AndroidJUnit4 you have to create a custom test runner where the screenshot stuff is initialized.

As described here: https://facebook.github.io/screenshot-tests-for-android/#custom-test-runner

Create a custom test runner in the test directory (androidTest/java/...):

public class MyTestRunner extends AndroidJUnitRunner {
  @Override
  public void onCreate(Bundle args) {
    ScreenshotRunner.onCreate(this, args);
    super.onCreate(args);
  }

  @Override
  public void finish(int resultCode, Bundle results) {
    ScreenshotRunner.onDestroy();
    super.finish(resultCode, results);
  }
}

In the build.gradle set the testInstrumentationRunner to your custom runner:

defaultConfig {
    // ...
    testInstrumentationRunner "my.package.MyTestRunner" 
}