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Payment Gateway

A Payment Gateway exercise in .NET.

Project Structure

src/
    PaymentGateway.Api - ASP.NET Core Web API project
test/
    PaymentGateway.Api.Tests - unit test project, using xUnit
    IntegrationTests - Postman collections for integration tests
imposters/ - contains the bank simulator configuration. Don't change this

.editorconfig - don't change this. It ensures a consistent set of rules for submissions when reformatting code
docker-compose.yml - configures the bank simulator
PaymentGateway.sln - the Visual Studio solution file

Implementation Details and Design Choices

  • The solution supports 3 different currency codes: GBP, EUR, USD.
  • A successful payment POST requests returns a 201 Created status, along with a JSON response model.
  • A POST request with invalid parameters returns a 400 Bad Request status, along with a JSON response model containing a "status": "Rejected" field, and a list of error messages.
  • Using the .NET buit-in logging library Microsoft.Extensions.Logging, and has been configured to output to the console and the debug provider.
  • The project uses the FluentValidation package for validating the payment request model. The reasons for using this instead of the built-in data annotations are:
    • It separates the validation logic from the API model
    • It offers better control over validation rules
    • The validation can be mocked in unit tests, if needed
  • Using the .NET built-in library System.Text.Json for parsing JSON.
  • The JSON naming convention for the Payment Gateway API models is camelCase, as it is the most commonly used in the industry.
  • The data models used for communicating with the acquiring bank service have JsonPropertyName attributes to configure the JSON field names to use the snake_case notation.
  • The HTTPClient instance used for calling the acquiring bank is instantiated only once per application, in order to allow it to reuse the same connection pool for multiple requests, and also prevent port exhaustion problems.
  • The PaymentsRepository is a singleton, to ensure that the same instance is used by all requests and that it is preserved for the whole lifetime of the application.

Local Development

Prerequisites

You need to have the following installed on your machine:

  • .NET SDK 8.0
  • Docker
  • Visual Studio 2022 (optional)
  • Postman (optional, for manually running integration tests) - download
  • Newman (optional, for running integration tests via CLI) - how to install

Start the Bank Simulator

Ensure that Docker is running on your machine. Open your terminal, and navigate to the project's root directory.

To start the simulator, run the following command:

docker-compose up

Run from Visual Studio

Open the PaymentGateway.sln solution file in Visual Studio.

Ensure that the PaymentGateway.Api project is configured as a startup project. To do this, right click the project, and from the context menu select the option Set as Startup Project. This will ensure that this project will run automatically when running the solution.

In the the top menu, click on Debug > Start Debugging or Debug > Start Without Debugging depending on your preference, or use one of the corresponding toolbar buttons.

Run from Terminal

In your terminal, navigate to the project's root directory.

dotnet run --project src/PaymentGateway.Api

Calling the locally running API

The project runs on the following ports: 7092 for HTTPS, and 5067 for HTTP.

The Payments API endpoint will be available at the following URL:

https://localhost:7092/api/payments

If you have Postman installed, you can import the following collection: test/IntegrationTests/PaymentsGateway.postman_collection.json

This has a several requests that verify the main requirements of the project. Ensure that you run the POST requests first, because the GET requests depend on them.

You can run the requests individually or in bulk by using the Run collection option.

Testing

Unit Testing

Option 1: Run from Visual Studio

With the solution open in Visual Studio, open the Test Explorer panel and click on the Run All Tests In View button.

Option 2: Run from Terminal

In your terminal, navigate to the project's root directory.

# list the unit tests:
dotnet test --list-tests test/PaymentGateway.Api.Tests

# run all the unit tests:
dotnet test test/PaymentGateway.Api.Tests

Integration Testing

Required: Newman CLI tool (more details in Prerequisites section)

First, start running the bank simulator and your project, as described in the above sections.

In your terminal, navigate to the project's root directory.

# Verifying that the bank simulator is running as expected
newman run -k test/IntegrationTests/PaymentsBankSimulator.postman_collection.json

# Integration tests for the Payment Gateway
newman run -k test/IntegrationTests/PaymentsGateway.postman_collection.json

Using the -k option disables SSL verification checks and allows self-signed SSL certificates, which is necessary when calling the localhost API URL on HTTPS.