NestJS, a popular framework for NodeJS projects built with TypeScript, supports building REST and GraphQL APIs, making it a preferred choice for teams adopting TypeScript. This tutorial demonstrates how to add unit and integration tests to a NestJS GraphQL project, specifically focusing on a sample invoicing application. The guide details the process of testing the customer module, including the setup for unit tests using Jest to mock dependencies like CustomerService and CustomerRepository, and end-to-end (E2E) tests that involve the complete stack without mocking. The tutorial also covers configuring TypeORM for a test database and automating the testing process with CircleCI, ensuring tests run whenever code changes are pushed to the repository. By integrating CircleCI, developers can automate their testing pipeline, thus maintaining application stability and functionality with each update.