Software Testing - Unit Testing Fundamentals

Unit Testing Fundamentals

Unit testing is the process of testing individual components of a software application in isolation to ensure they work as intended.
It’s usually the first level of testing in the Software Testing Life Cycle.

Key Points

  1. Purpose

    • Verify that each unit (function, method, class, or module) performs correctly.

    • Catch defects early before integration.

  2. Scope

    • Focuses only on the smallest testable parts of the application.

    • No interaction with databases, APIs, or external systems (unless mocked).

  3. Who Performs It

    • Usually developers (sometimes testers in technical teams).

  4. When Performed

    • During the coding phase, before integration testing.

Characteristics of Good Unit Tests

  • Isolated – No dependency on other modules or systems.

  • Repeatable – Produces the same result every time it runs.

  • Automated – Run automatically as part of the build process.

  • Fast – Quick to execute to encourage frequent testing.

Common Unit Testing Tools

  • Java: JUnit, TestNG

  • Python: unittest, pytest

  • JavaScript: Jest, Mocha

  • C#: NUnit, xUnit

Advantages

  • Detects bugs early.

  • Simplifies debugging (easy to pinpoint the problem).

  • Supports refactoring safely.

  • Improves code quality and maintainability.

Limitations

  • Does not test system-level behavior.

  • Requires time and effort to write and maintain.

  • May miss integration issues.