unittest is a built-in testing framework in Python that helps developers ensure their code works as intended. It allows users to create test cases, which are individual units of code that check specific functionality. By running these tests, developers can identify bugs and verify that changes to the code do not introduce new issues. The framework supports various testing methods, including assertions to compare expected outcomes with actual results. unittest also provides tools for organizing tests into suites, running them in isolation, and generating reports. This makes it easier to maintain code quality throughout the development process.