PyTorch, an open-source machine learning framework, facilitates the transition from research prototyping to production deployment without requiring knowledge of its underlying C++ code, offering tools for building machine learning applications with deep neural networks. This comprehensive tutorial demonstrates how to develop an image classification model using PyTorch's torchvision library and deploy it as a REST API through Flask, complemented by a series of pytest unit tests set up within a continuous integration pipeline using CircleCI. The guide also covers setting up a Python development environment, managing dependencies, and automating testing processes to ensure the model and API function correctly. By following detailed steps, including creating a Flask app with a prediction endpoint and testing API responses, users can automate workflows to enhance reliability and efficiency in machine learning development. The tutorial culminates in leveraging CircleCI for continuous integration, allowing for seamless testing and building of the PyTorch model and corresponding API, ultimately promoting faster prototyping and development.