What is Self-Testing?
Developing tests as part of the programming process is known as self-testing. Self-testing involves writing small pieces of code called unit tests to validate that specific sections of code—such as individual functions, classes, or methods—are working as intended. Each unit test focuses on testing a single "unit" of code in isolation from its surroundings. The goal is to thoroughly test each individual component so that when units are combined into full applications, interactions among components are less likely to introduce errors.

Why is Self-Testing Important?
Self-testing helps improve software quality and provides a number of important benefits for developers and organizations:

Early Error Detection
Unit Self-Testing are written while programming code, so errors can be found during development rather than later on. This allows issues to be fixed much more easily while code is fresh in the developer's mind. Finding and fixing bugs early saves a significant amount of time and money compared to discovering errors during integration, system testing, or in production use.

Prevents Regressions
Self-tests form a automated regression suite that can be easily run whenever code changes are made. This ensures existing functionality keeps working as intended and prevents previous bugs from re-emerging or new bugs from being introduced. Maintaining a comprehensive suite of tests provides a safety net that allows developers to refactor and optimize code freely.

Increases Code Quality
The act of writing tests forces developers to adhere to best practices like modularization, loose coupling, and high cohesion. Code must be designed for testability, which generally improves structure and readability. Self-tests also serve as living documentation that describes how code is intended to be used.

Enables Refactoring
Developers can confidently change code structure, make optimizations, or refactor large components when there is a complete safety net of regression tests. The tests act as a barrier against accidental changes or regressions. Extensive refactoring helps keep code high-quality and maintainable as a project evolves.

Get more insights, On Self-Testing