A .NET Core console application is used to send SMS messages using Twilio Programmable SMS. The application uses the Twilio helper library for .NET Core and stores its credentials securely as environment variables. It also sets up dependency injection using the .NET Core service provider. Additionally, it creates a test project and builds unit tests with the xUnit framework, including creating mocks for the SMS service using the Moq library. The application demonstrates how to use Twilio Programmable SMS in a real-world scenario and provides a foundation for learning about unit testing and dependency injection in .NET Core.