The Virtual Machine Test Harness (VMTH) is an automation tool that runs unit tests against a virtual machine running a live system image. It integrates with continuous integration servers to trigger tests after every code commit. The tool uses VM snapshotting to quickly run through test cases. It was created to help test configuration management like Puppet in a safe, isolated way compared to testing in production. The document outlines the VMTH workflow using Puppet as an example, describes the tools used like the virb interactive browsing tool, and provides resources for more information.