public async Task UpdateOrderTest() { // Arrange var args = new OrderUpdateArguments { OrderId = "order-id" }; _stripe.Post( Arg.Is <StripeRequest <OrderUpdateArguments, Order> >( a => a.UrlPath == "orders/" + args.OrderId && a.Model == args), _cancellationToken) .Returns(Task.FromResult(new StripeResponse <Order>())); // Act var response = await _client.UpdateOrder(args, _cancellationToken); // Assert response.Should().NotBeNull(); }