I have main.xml as follows:
  
     ...
     
          I have created a Hello World program on github for libgdx running in a fragment using Android Studio 2.1. It follows the instructions on the official libgdx wiki.
AndroidLauncher class:
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import com.badlogic.gdx.backends.android.AndroidFragmentApplication;
public class AndroidLauncher extends FragmentActivity implements  AndroidFragmentApplication.Callbacks {
    @Override
    public void onCreate (Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.layout);
        // Create libgdx fragment
        GameFragment libgdxFragment = new GameFragment();
        // Put it inside the framelayout (which is defined in the layout.xml file).
        getSupportFragmentManager().beginTransaction().
                add(R.id.content_framelayout, libgdxFragment).
                commit();
    }
    @Override
    public void exit() {
    }
}
The GameFragment class:
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import com.badlogic.gdx.backends.android.AndroidFragmentApplication;
public class GameFragment extends AndroidFragmentApplication{
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        // return the GLSurfaceView on which libgdx is drawing game stuff
        return initializeForView(new MyGdxGame());
    }
}
layout.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/main_layout"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <FrameLayout
    android:id="@+id/content_framelayout"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_weight="2">
    </FrameLayout>
    <TextView
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:background="#FF0000"
        android:textColor="#00FF00"
        android:textSize="40dp"
        android:text="I'm just a TextView here with red background :("/>
</LinearLayout>
MyGdxGame class:
import com.badlogic.gdx.ApplicationAdapter;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.graphics.Color;
import com.badlogic.gdx.graphics.GL20;
import com.badlogic.gdx.graphics.Texture;
import com.badlogic.gdx.graphics.g2d.BitmapFont;
import com.badlogic.gdx.graphics.g2d.SpriteBatch;
public class MyGdxGame extends ApplicationAdapter {
    SpriteBatch batch;
    Texture img;
    private BitmapFont font;
    @Override
    public void create () {
        batch = new SpriteBatch();
        img = new Texture("badlogic.jpg");
        font = new BitmapFont();
        font.setColor(Color.BLUE);
    }
    @Override
    public void render () {
        Gdx.gl.glClearColor(0, 0, 0, 0);
        Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
        batch.begin();
        //batch.draw(img, 0, 0);
        font.getData().setScale(6.0f);
        font.draw(batch, "Hello World from libgdx running in a fragment! :)", 100, 300);
        batch.end();
    }
    @Override
    public void dispose () {
        batch.dispose();
        img.dispose();
    }
}
Make sure you've added the following:
compile "com.android.support:support-v4:24.1.1"
To the project gradle script in the "dependencies {.}" section inside project (":android") section.
Using a libgdx project as a view inside an Android app is now documented clearly, with example code, in the libgdx wiki, implemented as a Fragment (the best practice for modern Android apps):
- Add Android V4 Support Library to the -android project and its build path if you haven't already added it. This is needed in order to Extend FragmentActivity later
 - Change AndroidLauncher activity to extend FragmentActivity, not AndroidApplication
 - Implement AndroidFragmentApplication.Callbacks on the AndroidLauncher activity
 - Create a Class that extends AndroidFragmentApplication which is the Fragment implementation for Libgdx.
 - Add the initializeForView() code in the Fragment's onCreateView method.
 - Finally, replace the AndroidLauncher activity content with the Libgdx Fragment.
 
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    AndroidApplicationConfiguration cfg = new AndroidApplicationConfiguration();
    cfg.useGL20 = false;
    //initialize(new LoveHearts(), cfg);
    LinearLayout lg=(LinearLayout)findViewById(R.id.game);
    lg.addView(initializeForView(new LoveHearts(), cfg));
}
                                                                        The AndroidApplication class (which extends activity) has a method named initializeForView(ApplicationListener, AndroidApplicationConfiguration) that will return a View you can add to your layout.
So your Test-class can extend AndroidApplication instead of Activity so that you can call that method and add the View to your layout.
If that's not an option, for some reason, take a look at what AndroidApplication source code does, and mimic that.