Large Language Models (LLMs) are increasingly being run locally on consumer-grade hardware, necessitating the need for reliable cross-operating system compatibility. This tutorial outlines how developers can set up an OS compatibility testing workflow using CircleCI matrix jobs, which automate the testing process across Linux, macOS, and Windows. By using Ollama, a tool for running LLMs locally, developers can ensure their applications function correctly on different operating systems without manual testing. The tutorial provides a step-by-step guide to installing Ollama on each OS using their respective package managers and running Python unit tests to verify functionality. By integrating these tests into a CI/CD pipeline, developers can catch platform-specific issues early, thereby enhancing the robustness and reliability of their applications across multiple environments. This approach can be adapted for various LLM projects to support different OS configurations and ensure seamless functionality.