В ответ на предложение @ kloffy:
package playground.tests;
import java.awt.GridLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import junit.framework.TestCase;
public class ButtonTest extends TestCase {
public void testThreeButtons() throws Exception {
JPanel panel = new JPanel();
panel.setLayout(new GridLayout());
JButton button1 = new JButton("A");
JButton button2 = new JButton("B");
JButton button3 = new JButton("C");
panel.add(button1);
panel.add(button2);
panel.add(button3);
JFrame window = new JFrame("Contacts");
window.setContentPane(panel);
window.setSize(300, 600);
window.pack();
window.setVisible(true);
int width = button1.getWidth();
assertEquals(width, button2.getWidth());
assertEquals(width, button3.getWidth());
}
}