TxnFlow Engine

A simple payment transaction simulation system built with Go.

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🚀 Features

• Create transaction
• Complete transaction using ISO 8583 response codes
• Transaction lifecycle:
  • PENDING → SUCCESS
  • PENDING → FAILED
• Idempotency handling
• Retry logic for issuer unavailable scenarios
• Transaction history tracking
• Playwright API regression tests

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📦 API Endpoints

Create Transaction

POST /transactions

Request: { "amount": 150000 }

Response: { "id": "TXN-xxxx", "amount": 150000, "status": "PENDING", "iso_code": "", "message": "Awaiting processor result" "idempotency_key": "unique-key" }

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Complete Transaction

POST /simulate/complete?id=TXN-xxxx

Request: { "iso_code": "51" }

Response: { "id": "TXN-xxxx", "amount": 150000, "status": "FAILED", "iso_code": "51", "message": "Insufficient funds" }

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🔁 Transaction Flow

Create Transaction → PENDING
↓
Complete Transaction
↓
SUCCESS (00) | FAILED (others) | RETRY (91)

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🧠 ISO 8583 Codes

00 → Approved
14 → Invalid card
51 → Insufficient funds
54 → Expired card
91 → Issuer unavailable

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🛠 Tech Stack

• Go (net/http)
• Playwright (API Testing)
• In-memory storage (map)

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▶️ Run Locally

Start backend:

go run .

Run Playwright API tests:

npx playwright test

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🧪 Test Coverage

• Create transaction success
• Idempotency validation (same request returns same transaction)
• Retry scenario (ISO 91 → RETRY)
• Full flow regression (PENDING → SUCCESS with history validation)

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🎯 Purpose

This project simulates real-world payment transaction flows, including:

• Status transitions
• Failure handling
• ISO 8583 response mapping

Built to demonstrate system-level thinking for SDET / QA Automation roles.