A proper cleanup of http://qathread.blogspot.com/2014/09/discovering-espresso-for-android-how-to.html for Espresso 2.0

CurrentActivityUtil.java

import android.app.Activity;
import android.support.annotation.Nullable;
import android.support.test.runner.lifecycle.ActivityLifecycleMonitorRegistry;

import java.util.Collection;

import static android.support.test.InstrumentationRegistry.getInstrumentation;
import static android.support.test.runner.lifecycle.Stage.RESUMED;

public final class CurrentActivityUtil {

    @Nullable
    public static Activity getCurrentActivity() {
        final Activity[] currentActivity = {null};
        getInstrumentation().runOnMainSync(() -> {
            Collection<Activity> resumedActivities = ActivityLifecycleMonitorRegistry.getInstance().getActivitiesInStage(RESUMED);
            if (resumedActivities.iterator().hasNext()) {
                currentActivity[0] = resumedActivities.iterator().next();
            }
        });

        return currentActivity[0];
    }
}