test: Unit & integration tests for KorapayGateway

[teesofttech]

Overview

Add a complete unit and integration test suite for KorapayGateway.

Gateway Details

• Class: KorapayGateway
• Region: Nigeria / Africa
• Auth: Bearer token (SecretKey)
• Base URL: https://api.korapay.com/merchant/api/v1/
• Tx Ref prefix: KR_ (from GatewayReferencePrefixes.Korapay)
• Enum: PaymentGatewayType.Korapay = 9

Unit Tests (mocked HTTP)

Constructor

• Throws InvalidOperationException when SecretKey is null/whitespace
• Sets BaseAddress to https://api.korapay.com/merchant/api/v1/
• Sets Authorization: Bearer header

CreatePaymentAsync

• Posts to /charges/initialize with correct payload (reference, amount, currency, customer.email, redirect_url)
• Reference starts with KR_
• Returns PaymentResponse.Success=true with CheckoutUrl (data.checkout_url) on success
• Returns PaymentResponse.Success=false when data.status=false

VerifyPaymentAsync

• Sends GET /charges/{reference}
• Returns IsSuccessful=true when data.status=success
• Returns IsSuccessful=false for failed/processing

RefundPaymentAsync

• Posts to /refunds with correct payload
• Returns RefundResponse.IsSuccessful=true on success

GatewayExtractor Tests

• DetectGatewayFromWebhook returns PaymentGatewayType.Korapay when reference starts with KR_

Integration Tests

Requires KORAPAY_SECRET_KEY env var

• CreatePaymentAsync returns a real Korapay checkout URL

Files to Create

• PayBridge.SDK.Test/Unit/KorapayGatewayTests.cs
• PayBridge.SDK.Test/Integration/KorapayIntegrationTests.cs

Acceptance Criteria

• All unit tests pass with zero live HTTP calls
• Integration tests use [Trait("Category", "Integration")] and skip when env var is absent
• Code coverage >= 80% for KorapayGateway.cs