public void GetAll_ReturnsAll_ForSpecificUser()
{
target.AddUpdate("User1", new PaymentMethod { Id = "paymentMethod1" });
target.AddUpdate("User2", new PaymentMethod { Id = "paymentMethod2" });
target.AddUpdate("User2", new PaymentMethod { Id = "paymentMethod3" });
Assert.AreEqual(1, target.GetAll("User1").Count());
Assert.AreEqual(2, target.GetAll("User2").Count());
}