public async Task UpdateInvoiceItemTest() { // Arrange var args = new InvoiceItemUpdateArguments { InvoiceItemId = "invoiceitem-id" }; _stripe.Post( Arg.Is <StripeRequest <InvoiceItemUpdateArguments, InvoiceItem> >( a => a.UrlPath == "invoiceitems/" + args.InvoiceItemId && a.Model == args), _cancellationToken) .Returns(Task.FromResult(new StripeResponse <InvoiceItem>())); // Act var response = await _client.UpdateInvoiceItem(args, _cancellationToken); // Assert response.Should().NotBeNull(); }