What is NUnit and how does it work in .NET testing?

Short answer: NUnit is a popular open-source unit testing framework for .NET. It allows developers to write and run automated tests by marking test methods with attributes. NUnit discovers and executes these tests, verifying that the code behaves as expected.

Real-world example (ShopNest)

ShopNest unit tests cover pricing and discount rules so a bad coupon change fails in CI before customers see it.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.