# Test Stacks Every Testery Test Run has a **Test Stack.** A Test Stack is a collection of operating systems and softwares to enable your Test Framework to run. A full list of supported Test Stacks is available in the Testery app You never need to specify a Test Stack - if you don't provide one, a default stack will be selected for you. However, you have the ability to control the versions of Node.js and Chrome that your tests will run against by providing a testery.yml file in your source repository. For example, a Cypress run might be assigned, by default, to the `node-chrome.120-java.17-nodejs.18` test stack. This uses Node.js 18 and Chrome 120. If you wanted to test your code against Chrome 121, you would provide the following in your testery.yml file. ``` test_stack: configuration_key: node-chrome.121-java.17-nodejs.18 ``` One benefit of this approach is allowing you to test new versions of dependencies on a branch. Testery will respect the testery.yml file in your branch, allowing you to fix issues on your branch, while using the default Test Stack on your `main` branch. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.testery.io/get-to-know-testery/test-stacks.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.