MXUnit is a unit testing framework for CFML that allows developers to write automated tests for their applications. Key features include directory runner for running all tests in a folder, support for different output formats, and built-in assertions for validating test results. Tests are written as test cases in CFC files, which can contain setup/teardown functions as well as individual test methods. Data providers allow test cases to run with different sets of data. MXUnit also supports testing private methods and includes utilities for debugging tests.