private static void MakeChanges(Period period, Amount amount = null, Label label = null, Pair pair = null, SpendingCategory category = null)
 {
     period.ChangeSpending(OperationId.From(1),
                           amount ?? Amount.From(10),
                           label ?? Label.From("test"),
                           pair ?? Pair.First,
                           category ?? SpendingCategory.Advance);
 }