public void AddCardToWallet(int wallet, string cardName, double interest, double balance)
{
sut.People.Add(user1Mock.Object);
sut.People.Add(user2Mock.Object);
sut.AddCardToWallet(username1, wallet, cardName, interest, balance);
user1Mock.Verify(x => x.AddCard(wallet, cardName, interest, balance), Times.Once);
user2Mock.Verify(x => x.AddCard(wallet, cardName, interest, balance), Times.Never);
}