private async Task <(string AckUrl, Guid Otc, string Password)> Pay(Pocket p, int amount, string pocketAckUrl, SimpleFilter filter = null)
{
int beforeCount = p.VoucherCount;
(var otcPay, var pwd) = await _pos.RequestPayment(amount, pocketAckUrl, "https://example.org", filter, false);
var ret = await p.PayWithRandomVouchers(otcPay, pwd);
Assert.AreEqual(beforeCount - amount, p.VoucherCount);
return(ret, otcPay, pwd);
}