Mocha is an open-source JavaScript testing framework designed for Node.js and browser environments, enabling developers to test both synchronous and asynchronous code through a straightforward interface. It executes tests serially for accurate reporting and maps uncaught exceptions to their respective test cases, ensuring that each test runs independently. Mocha is often paired with the Chai assertion library to enhance testing capabilities and supports Behavior-Driven Development (BDD) interfaces for defining test suites, hooks, and individual tests. The framework allows for flexible testing configurations, including handling asynchronous operations via callbacks, Promises, and async/await syntax, as well as providing options for test hooks, retries, and timeout settings. Mocha's CLI offers numerous tools for running tests, adjusting timeouts, and managing test execution, while its functionality extends to browser environments through specific setup processes.