What is xUnit and why is it popular in .NET testing?

Short answer: xUnit is a free, open-source unit testing framework for .NET, designed by the original authors of NUnit. It’s popular because it supports modern testing practices, is lightweight, extensible, integrates well with .NET Core and Visual Studio, and encourages clean, maintainable test code.

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.