test: Unit & integration tests for SquadGateway

[teesofttech]

Overview

Add a complete unit and integration test suite for SquadGateway.

Gateway Details

• Class: SquadGateway
• Region: Nigeria (by GTCo)
• Auth: Static Bearer token (SecretKey)
• Sandbox URL: https://sandbox-api-d.squadco.com
• Live URL: https://api-d.squadco.com
• Config: SecretKey, IsSandbox flag
• Enum: PaymentGatewayType.Squad = 8

Unit Tests (mocked HTTP)

Constructor

• Throws InvalidOperationException when SecretKey is null/empty
• Uses SandboxUrl when IsSandbox=true
• Uses LiveUrl when IsSandbox=false

CreatePaymentAsync

• Posts to /transaction/initiate with correct payload (amount in kobo, email, currency=NGN, initiate_type=inline)
• Sets Authorization: Bearer header
• Returns PaymentResponse.Success=true with CheckoutUrl (checkout_url) on success
• Returns PaymentResponse.Success=false on API failure

VerifyPaymentAsync

• Sends GET /transaction/verify/{reference}
• Returns IsSuccessful=true when transaction_status=success
• Returns IsSuccessful=false for failed/pending

RefundPaymentAsync

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

Integration Tests

Requires SQUAD_SECRET_KEY env var and SQUAD_IS_SANDBOX=true

• CreatePaymentAsync returns a real Squad checkout URL
• VerifyPaymentAsync returns correct status

Files to Create

• PayBridge.SDK.Test/Unit/SquadGatewayTests.cs
• PayBridge.SDK.Test/Integration/SquadIntegrationTests.cs

Acceptance Criteria

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