### Question:
Stack { public boolean isEmpty() { return list.isEmpty(); }  void push(T o); T pop(); T replaceTop(T value); T peek(); boolean isEmpty(); int size(); List<T> getList(); static final Stack EMPTY; }### Answer:
@Test public void testIsEmpty() throws Exception { assertTrue(stack.isEmpty()); stack.push("a"); assertFalse(stack.isEmpty()); stack.pop(); assertTrue(stack.isEmpty()); }