What feature allows for increased maintainability in code structure?

Implementing unit testing enhances code maintainability by ensuring that individual components of the codebase function correctly in isolation. Unit tests provide a safety net that verifies that changes made to the code do not break existing functionality. With comprehensive unit tests, developers can confidently refactor their code, knowing that the tests will catch any errors that may arise from their modifications.

Additionally, unit tests serve as documentation for the code's intended behavior, making it easier for current and future developers to understand the purpose of functions and the expected outcomes. This reduces the time needed to maintain and update the code over time, as clear tests communicate the desired functionality and constraints of the code.

While using global variables can lead to easier data sharing across functions, it can also result in tightly coupled code that is hard to debug and maintain. Restricting function returns may limit functionality and increase complexity. Writing large monolithic functions typically leads to code that is difficult to understand, test, and maintain, as the interdependencies can make it challenging to isolate problems. In contrast, unit testing supports a modular approach that significantly improves the maintainability of code.