What is unit testing, and how does Test-Driven Development (TDD) change the workflow?

What is unit testing, and how does Test-Driven Development (TDD) change the workflow?

• A. Unit testing verifies small pieces of code; TDD writes tests before code and uses them to drive development.
• B. Unit testing checks the entire system integration.
• C. TDD eliminates the need for tests.
• D. TDD postpones testing until after code is written.

Answer: (A)

Unit testing focuses on small pieces of code in isolation to verify they behave correctly. When you bring in Test-Driven Development, you start by writing a test that defines the desired behavior, then you implement the minimal code needed to pass that test, and finally you refine the code. This creates a loop where tests guide what you build and stay as a safety net as the code evolves. It’s about testing early and often, rather than testing the whole system at once or waiting to test after everything is written. That’s why this description best fits: unit testing verifies small pieces of code, and TDD writes tests before code and uses them to drive development.