What is a key characteristic of unit tests?

A key characteristic of unit tests is that they test individual units for correct functionality. A unit test typically focuses on a small part of the application, such as a single function or method, ensuring that it performs as expected under various conditions. This isolation allows developers to pinpoint issues in specific parts of the codebase quickly and ensures that changes or refactoring do not break existing functionalities. By validating the smallest testable parts of an application, unit tests contribute significantly to the overall quality and maintainability of the code.

In contrast, other approaches, such as evaluating entire applications (which would be more characteristic of integration or system testing) and replacing integration testing, do not align with the primary purpose of unit tests. While they help ensure that individual components work correctly, unit tests do not address interactions between those components. Additionally, unit tests are not aimed at identifying security vulnerabilities; that is typically the role of security testing or specific tools designed for that purpose.