public void Create_ItShouldCreateABill()
        {
            var obj = RecurringBill.Create(
                groupId: "cld-3",
                priceCents: 1500,
                description: "Some Bill"
                );

            Assert.IsNotNull(obj.Id);
            Assert.IsNotNull(obj.CreatedAt);
        }
        public void Cancel_ItShouldCancelABill()
        {
            var obj = RecurringBill.Create(
                groupId: "cld-3",
                priceCents: 1500,
                description: "Some Bill"
                );
            var updatedAt = obj.UpdatedAt;

            obj.Cancel();
            Assert.AreEqual("cancelled", obj.Status);
            Assert.IsTrue(obj.UpdatedAt.HasValue);
        }