public void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {                                         
  //JOptionPane.showConfirmDialog(null, "Text", "text", JOptionPane.PLAIN_MESSAGE);
   float a = Float.parseFloat(jTextField1.getText());
   float b = Float.parseFloat(jTextField2.getText());
   jTextField3.setText(String.valueOf(a/b));

package test;

import static org.junit.Assert.*;

import org.junit.Test;

public class TESTJF {

	@Test
	public void testJButton2ActionPerformed() {		
      //НУЖНА ПОМОЩЬ ЗДЕСЬ
		//fail("Еще не реализовано");
	}

}

JF a = new JF();

public class JF extends javax.swing.JFrame {

    /**
     * Creates new form JF
     */
    public JF() {
        initComponents();
    }