public void Test1_2_Should_Be_Empty_After_Pop()
 {
     var bookSet = new BookSet(1, 2);
     var result = bookSet.PopCart(5);
     result = bookSet.PopCart(5);
     Assert.That(result, Is.EquivalentTo(new int[] {}));
 }
 public void Test1_2()
 {
     var bookSet = new BookSet(1, 2);
     var result = bookSet.PopCart(5);
     Assert.That(result, Is.EquivalentTo(new[] { 1, 2 }));
 }