tests: this commit introduces a mock for the payment gateway

Author: https-richardy

Boundaries/Comanda.Payments/Tests/Mocks/PaymentGatewayMock.cs

@@ -0,0 +1,16 @@
+namespace Comanda.Payments.TestSuite.Mocks;
+
+public sealed class PaymentGatewayMock : IPaymentGateway
+{
+    public Task<Result<CheckoutSession>> CreateCheckoutSessionAsync(
+        CheckoutSessionCreationScheme parameters, Payment payment, CancellationToken cancellation = default)
+    {
+        var session = new CheckoutSession
+        {
+            Code = $"brcode_{Guid.NewGuid():N}",
+            QrCode = $"qrcode_{Guid.NewGuid():N}"
+        };
+
+        return Task.FromResult(Result<CheckoutSession>.Success(session));
+    }
+}