JComponent not showing in JPanel

Question

I've tried the add() method but nothing is displayed when I try to add Test to GraphicsTest. How should I be adding it? Can someone show me? I've included the code I'm using.
This is my way and it's not working. Can someone show me or make me aware of what the problem actually is?
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.Rectangle2D;
import javax.swing.JPanel;
public class GraphicsTest extends JPanel
    private Graphics2D g2d;
    private String state;
    private int x, y;
    GraphicsTest()
        Test t = new Test();
        t.setVisible(true);
        add(t);
    @Override
    public void paintComponent(Graphics g)
        super.paintComponent(g);
        g2d = (Graphics2D) g;
        g2d.setColor(Color.BLACK);
        g2d.drawString("STATE: " + state, 5, 15);
        g2d.drawString("Mouse Position: " + x + ", " + y, 5, 30);
        g2d.setColor(Color.red);
        Rectangle2D r2d = new Rectangle2D.Double(x, y, 10, 10);
        g2d.draw(r2d);
        g2d.dispose();
    public void setState(String state) { this.state = state; }
    public String getState() { return state; }
    public void setX(int x) { this.x = x; repaint(); }
    public void setY(int y) { this.y = y; repaint(); }
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JComponent;
public class Test extends JComponent
    @Override
    public void paintComponent(Graphics g)
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g.create();
        g2d.setColor(Color.red);
        g2d.drawString("Hello", 50, 50);
        g2d.dispose();
}

Answer 1

The object in Test ("hello") is not appearing.
import java.awt.EventQueue;
//import java.awt.event.MouseEvent;
//import java.awt.event.MouseListener;
//import java.awt.event.MouseMotionListener;
import javax.swing.JFrame;
public class MainWindow
    public static void main(String[] args)
        new MainWindow();
    JFrame frame;
    GraphicsTest gt = new GraphicsTest();
    MainWindow()
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                frame = new JFrame("Graphics Practice");
                frame.setSize(680, 420);
                frame.setVisible(true);
                frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
//                gt.addMouseListener(new MouseListener() {
//                    public void mouseClicked(MouseEvent e) {}
//                    public void mousePressed(MouseEvent e) {}
//                    public void mouseReleased(MouseEvent e) {}
//                    public void mouseEntered(MouseEvent e) {
//                        gt.setState("Mouse has entered");
//                    public void mouseExited(MouseEvent e) {
//                        gt.setState("Mouse has not entered");
//                gt.addMouseMotionListener(new MouseMotionListener() {
//                    public void mouseDragged(MouseEvent e) {}
//                    public void mouseMoved(MouseEvent e) {
//                        gt.setX(e.getX());
//                        gt.setY(e.getY());
                frame.add(gt);
}