Solución a la segunda parte del examen, con pruebas automatizadas agregadas.

Baraja.java

package parte2;

import java.util.ArrayList;
import java.util.Collections;

/**
 * @author lfborjas
 */
public class Baraja {
    public static String[] palos={"diamantes", "tréboles", "corazones", "espadas"};
    private ArrayList<Carta> cartas;
    public Baraja(){
        cartas = new ArrayList<Carta>();
        for(String palo: palos)
            for(int i=1;i<=13;i++)
                cartas.add(new Carta(palo, i));

    }

    public void barajar(){
        Collections.shuffle(cartas);
    }

    public ArrayList<Carta> sacar(int n){
        ArrayList<Carta> rv = new ArrayList<Carta>();
        for(int i=0;i<n;i++)
            rv.add(cartas.remove(0));
        return rv;
    }

    public Carta sacar(){
        return cartas.remove(0);
    }

    public ArrayList<Carta> getCartas(){
        return this.cartas;
    }

    public String toString(){
        return cartas.toString();
    }

}

BarajaTest.java

package parte2;

import java.util.ArrayList;
import java.util.Random;
import junit.framework.TestCase;

/**
 *
 * @author lfborjas
 */
public class BarajaTest extends TestCase {
    
    public BarajaTest(String testName) {
        super(testName);
    }

    @Override
    protected void setUp() throws Exception {
        super.setUp();
    }

    @Override
    protected void tearDown() throws Exception {
        super.tearDown();
    }

    
    /**
     * Test of sacar method, of class Baraja.
     */
    public void testSacar_int() {
        System.out.println("sacar");
        Random gen = new Random();
        int n = gen.nextInt(52);
        Baraja instance = new Baraja();        
        ArrayList result = instance.sacar(n);

        assertEquals(n, result.size());
        System.out.println(result);
        assertEquals(52-n, instance.getCartas().size());
    
    }

    /**
     * Test of sacar method, of class Baraja.
     */
    public void testSacar_0args() {
        System.out.println("sacar");
        Baraja instance = new Baraja();
        Carta expResult = null;
        Carta result = instance.sacar();
        assertEquals(52-1, instance.getCartas().size());
        System.out.println(result);
    
    }

    
}

Carta.java

package parte2;

import java.util.ArrayList;
import java.util.HashMap;
/**
 * @author lfborjas
 */
public class Carta {
    private String palo;
    private int numero;

    public Carta(String palo, int numero){
        this.palo = palo;
        this.numero = numero;
    }

    @Override
    public String toString(){
        return String.format("%s de %s", getRankDisplay(), palo);
    }

    public String getRankDisplay(){
        switch(this.numero){
            case 1:
                return "as";
            case 11:
                return "sota";
            case 12:
                return "reina";
            case 13:
                return "rey";
            default:
                return String.valueOf(numero);
        }
    }

    public boolean equals(Carta otra){
        return this.palo.equals(otra.palo) && this.numero == otra.numero;
    }

    public static String getSerie(ArrayList<Carta> mano){
        int mayorPalo=0;
        int mayorNum=0;
        HashMap<Integer, Integer> numeros = new HashMap<Integer, Integer>();
        HashMap<String, Integer> palos = new HashMap<String, Integer>();
        for(Carta c: mano){
            int add = palos.get(c.palo)!= null ?  palos.get(c.palo)+1 : 1 ;
            palos.put(c.palo, add);
            add = numeros.get(c.numero) != null ? numeros.get(c.numero)+1: 1;
            numeros.put(c.numero, add);
        }
        for(Integer e: palos.values()){
            mayorPalo = e > mayorPalo ? e : mayorPalo;
        }
        
        for(Integer e: numeros.values()){
            mayorNum = e > mayorNum ? e : mayorNum;
        }

        StringBuilder retVal = new StringBuilder();       
        if(mayorPalo == mano.size())
            return "flush";
        if(mayorNum == mano.size() -1)
            return "poker";
        return "ninguna";
    }

    public static int getCuenta(ArrayList<Carta> mano){
        int c=0;
        boolean hasAce=false;
        for(Carta k: mano){
            switch(k.numero){
                case 1:
                    c += 11;
                    hasAce = true;
                    break;
                case 11:
                case 12:
                case 13:
                    c += 10;
                    break;
                default:
                    c += k.numero;
            }
        }
        if(c >= 21 && hasAce)
            return c-10;
        else
            return c;

    }
}

CartaTest.java

package parte2;

import java.util.ArrayList;
import java.util.Collections;
import junit.framework.TestCase;

/**
 *
 * @author lfborjas
 */
public class CartaTest extends TestCase {
    
    public CartaTest(String testName) {
        super(testName);
    }

    @Override
    protected void setUp() throws Exception {
        super.setUp();
    }

    @Override
    protected void tearDown() throws Exception {
        super.tearDown();
    }

    /**
     * Test of toString method, of class Carta.
     */
    public void testToString() {
        System.out.println("toString");
        Carta[] instances = {new Carta("diamantes", 11),
                             new Carta("diamantes", 12),
                             new Carta("diamantes", 13),
                             new Carta("diamantes", 1),
                             new Carta("diamantes", 5),
        };
        String[] expResults = {"sota de diamantes",
                               "reina de diamantes",
                               "rey de diamantes",
                               "as de diamantes",
                               "5 de diamantes",
        };
        for(int i=0; i < instances.length; i++)
            assertEquals(instances[i].toString(), expResults[i]);
               
    }

    /**
     * Test of equals method, of class Carta.
     */
    public void testEquals() {
        System.out.println("equals");
        Carta otra = new Carta("corazones", 11);
        Carta otra2 = new Carta("corazones", 12);
        Carta otra3 = new Carta("espadas", 11);
        Carta instance = new Carta("corazones", 11);

        assertTrue(instance.equals(otra));
        assertFalse(instance.equals(otra2));
        assertFalse(instance.equals(otra3));
   }

    /**
     * Test of getSerie method, of class Carta.
     */
    public void testGetSerie() {
        System.out.println("getSerie");
        ArrayList<Carta> manoFlush = new ArrayList<Carta>();
        ArrayList<Carta> manoPoker = new ArrayList<Carta>();
        ArrayList<Carta> manoNil = new ArrayList<Carta>();

        //llenar el flush:
        manoFlush.add(new Carta("diamantes", 1));
        manoFlush.add(new Carta("diamantes", 9));
        manoFlush.add(new Carta("diamantes", 10));
        manoFlush.add(new Carta("diamantes", 12));
        manoFlush.add(new Carta("diamantes", 11));
        Collections.shuffle(manoFlush);

        //poker:
        manoPoker.add(new Carta("diamantes", 1));
        manoPoker.add(new Carta("espadas", 1));
        manoPoker.add(new Carta("corazones", 1));
        manoPoker.add(new Carta("tréboles", 1));
        manoPoker.add(new Carta("diamantes", 12));
        Collections.shuffle(manoFlush);

        //esta mano no es ni poker ni flush
        manoNil.add(new Carta("corazones", 1));
        manoNil.add(new Carta("espadas", 1));
        manoNil.add(new Carta("tréboles", 1));
        manoNil.add(new Carta("diamantes", 1));
        manoNil.add(new Carta("corazones", 1));
        Collections.shuffle(manoNil);

        assertEquals("flush", Carta.getSerie(manoFlush));
        assertEquals("poker", Carta.getSerie(manoPoker));
        assertEquals("ninguna", Carta.getSerie(manoNil));

    }

    /**
     * Test of getCuenta method, of class Carta.
     */
    public void testGetCuenta() {
        System.out.println("getCuenta");
        ArrayList<Carta> manoSinAs = new ArrayList<Carta>();
        ArrayList<Carta> mano = new ArrayList<Carta>();
        //una mano con un as que la hace pasarse de 21:
        mano.add(new Carta("corazones", 11));
        mano.add(new Carta("corazones", 1));

        //una mano normal
        manoSinAs.add(new Carta("corazones", 12));
        manoSinAs.add(new Carta("corazones", 13));
        manoSinAs.add(new Carta("corazones", 7));

        assertEquals(11, Carta.getCuenta(mano));
        assertEquals(27, Carta.getCuenta(manoSinAs));
        
    }

}

Main.java

package parte2;

import java.util.ArrayList;
import javax.swing.JOptionPane;

/**
 *
 * @author lfborjas
 */
public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        boolean consent=true;
        Baraja baraja = new Baraja();
        baraja.barajar();
        ArrayList<Carta> sacadas;
        sacadas = baraja.sacar(5);
        do{
            
            JOptionPane.showMessageDialog(null,
                                          String.format("Cartas sacadas:\n%s",sacadas));

            JOptionPane.showMessageDialog(null,
                                          String.format("¿Serie especial?:\n%s",Carta.getSerie(sacadas)));

            JOptionPane.showMessageDialog(null,
                                          String.format("Cuenta:\n%d",Carta.getCuenta(sacadas)));
            consent = JOptionPane.showConfirmDialog(null, "Desea salir?",
                                                "¿Desea salir?",
                                                JOptionPane.YES_NO_OPTION) == 0;
            if(baraja.getCartas().size() >= 5)
                sacadas = baraja.sacar(5);
            else
                consent = true;
        }while(!consent);
    }
}