How do I provide a custom Application class to my Espresso Activity test?

I'm pretty new to Espresso, but I am trying to test a relatively simple Activity. My android app has its own custom Application class. How can I tell Espresso to use a mocked (or custom) version of this class?

Here is my custom version of the Application. It creates some test data (edited here for brevity). Down the road, I will also be overriding some of the methods.

public class MockMyApplication extends MyApplication {

@Override
public void onCreate() {
    super.onCreate();

    // create some location data for testing
    DataRecord rec = new DataRecord(1);
    rec.setName("TestLoc1");
    rec.setDescription("an important customer");
    MyData.add(rec);
 }
}

My attempt to test using this, looks like this:

@RunWith(AndroidJUnit4.class)
@LargeTest
public class LocEditActivityTest extends AndroidJUnitRunner {

@Rule
public ActivityTestRule<LocEditActivity> activityTestRule
        = new ActivityTestRule<>(LocEditActivity.class);


@Override
public Application newApplication(ClassLoader cl, String className, Context context) throws IllegalAccessException, ClassNotFoundException, InstantiationException {
    return super.newApplication(cl, MockMyApplication.class.getName(), context);
}


@Test
public void testActivity_ExistingLoc() {

    Intent i = new Intent();
    i.putExtra("loc",1);
    activityTestRule.launchActivity(i);

    onView(withId(R.id.editName)).check(matches(withText("TestLoc1")));


    // shutdown
    onView(withContentDescription("Navigate up")).perform(click());

 }
}

Using a debugger, I have determined that when LocEditAcitivity's onCreate calls getApplication(), it returns a MyApplication class with empty data, and not the MockedMyApplication with my test data.

Found it!

Looks like I misunderstood the "Runner" class usage. I needed to create my own Runner that extended AndroidJUnitRunner:

import android.app.Application;
import android.content.Context;
import android.support.test.runner.AndroidJUnitRunner;


// Our own test runniner - uses MockMyApplication as a mocked app class
public class MyAndroidTestRunner extends AndroidJUnitRunner {

    @Override
    public Application newApplication(ClassLoader cl, String className, Context context) throws IllegalAccessException, ClassNotFoundException, InstantiationException {
        return super.newApplication(cl, MockMyApplication.class.getName(), context);
    }

}

And then in build.gradle (app), the testInstrumentationRunner entry needs to point to the new runner:

        testInstrumentationRunner "com.winwaed.xyzapp.MyAndroidTestRunner"

As the newApplication override was in the wrong place, this should be removed from my test class. Also, the test class no longer extends any classes. (ie. I essentially split the runner and test classes - as I said, I misunderstood the runner class)