public void Test_Method_LibraryBookIncreaseQuantityBy()
{
Book k = new Book();
k.Title = "Sto godina samoce";
k.ISBN = "ISBN 1-12345-123-1";
k.Publisher = "Sarajevo publishing";
LibraryBook lk = new LibraryBook(k);
lk.Quantity = 100;
lk.IncreaseQuantityBy(5);
Assert.AreEqual(Convert.ToUInt32(105), lk.Quantity);
}