Added tests fir deckOFCards class

src/test/java/edu/ntnu/stud/cardgame/DeckOfCardsTest.java

+package edu.ntnu.stud.cardgame;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class DeckOfCardsTest {
+  DeckOfCards deck;
+
+  @BeforeEach
+  void setDeck() {
+    deck = new DeckOfCards();
+  }
+
+  @Nested
+  public class PositiveTests{
+    @Test
+    void testDeckFiller(){
+      assertEquals(deck.getDeck().size(), 52);
+      assertTrue(deck.getDeck().contains(new PlayingCard('H', 10)));
+      assertTrue(deck.getDeck().contains(new PlayingCard('D', 1)));
+      assertTrue(deck.getDeck().contains(new PlayingCard('C', 5)));
+    }
+  }
+}