feat: added DeckTest class

src/test/java/hepia/DeckTest.java

 package hepia;
 
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
 public class DeckTest {
+    @Test
+    public void invalidDeckCreation() {
+        int nbCards = 5; // invalid number of cards for creating a deck of cards
+        assertThrows(RuntimeException.class, () -> new Deck(5));
+    }
+
+    @Test
+    public void validDeckCreation() {
+        int nbCards = 32; // valid number of cards for creating a deck of cards
+        assertDoesNotThrow(() -> new Deck(nbCards));
+    }
 }