AVA is a test runner for Node.js. Even though JavaScript is single-threaded, IO in Node.js can happen in parallel because of its asynchronous nature. AVA takes advantage of this and runs your tests concurrently, which is especially beneficial for IO-heavy tests. In addition, test files are run in parallel as separate processes, giving you even better performance and an isolated environment for each test file. AVA is a lightweight option, when compared to full-featured frameworks such as Jest. It is opinionated and forces you to write atomic test cases.