### Question:
IntSinglyLinkedList implements Serializable, Iterable<Integer> { public void addFirst(int item) { IntNode n = new IntNode(item, head); size++; if(head == null) { head = tail = n; } else { head = n; } } IntSinglyLinkedList(); int size(); boolean contains(int item); void addLast(int item); void addFirst(int item); boolean isEmpty(); void clear(); int pop(); int peek(); void push(int item); int dequeue(); int getFirst(); void enqueue(int item); int[] toArray(); Integer[] toObjArray(); @Override String toString(); @Override boolean equals(Object other); @Override int hashCode(); @Override IntListIterator iterator();  }### Answer:
@Test public void testAddFirst() { IntSinglyLinkedList list = new IntSinglyLinkedList(); list.addFirst(0); list.addFirst(1); assertEquals(1, list.peek()); }