card-game/src/PileTest.java

import org.junit.jupiter.api.Test;

import java.util.Random;

import static org.junit.jupiter.api.Assertions.*;

class PileTest {

    @Test
    void shuffleEmptyPile() {
        Pile pile = new Pile();
        pile.shuffle();
        assertEquals(0, pile.size());
    }

    @Test
    void shuffleOneCard() {
        Pile pile = new Pile();
        pile.add(new Card(1, Card.Suit.CLUBS));
        pile.shuffle();
        assertEquals(1, pile.size());
        assertEquals(1, pile.size());
    }

    @Test
    void shuffleCards() {
        Pile pile = new Pile();
        pile.add(new Card(1, Card.Suit.CLUBS));
        pile.add(new Card(2, Card.Suit.DIAMONDS));
        pile.add(new Card(3, Card.Suit.HEARTS));
        pile.add(new Card(4, Card.Suit.SPADES));
        Random random = new Random(1);
        pile.shuffle(random);
        assertEquals(4, pile.get(0).number);
        assertEquals(Card.Suit.SPADES, pile.get(0).suit);
        assertEquals(1, pile.get(1).number);
        assertEquals(Card.Suit.CLUBS, pile.get(1).suit);
        assertEquals(2, pile.get(2).number);
        assertEquals(Card.Suit.DIAMONDS, pile.get(2).suit);
        assertEquals(3, pile.get(3).number);
        assertEquals(Card.Suit.HEARTS, pile.get(3).suit);
        assertEquals(4, pile.size());
    }
}