What is a unit test?

A unit test is specifically designed to isolate and verify the functionality of individual units of source code, such as functions, methods, or classes. This type of testing is fundamental in a test-driven development (TDD) approach, where developers write tests for specific pieces of code before implementing the actual code. The purpose of a unit test is to ensure that each part of the program behaves as intended when supplied with specific inputs.

By focusing on small code units, developers can detect errors early in the development cycle, making it easier to isolate problems within specific components rather than having to analyze larger portions of the codebase. This leads to increased reliability and maintainability of the software over time, as each unit can be independently tested and modified without affecting other parts of the application.

In contrast to unit tests, tests that evaluate the entire application as a whole assess the integration and interaction of all components rather than their individual functionality. Assessing user interactions with the product involves usability testing and is not focused on code verification. A diagnostic test for identifying team skills would pertain to evaluating team capabilities instead of the performance of specific code units. Each of these options points to different levels and types of testing that address various aspects of software development, but only the identification and validation