What tools and frameworks support TDD in .NET?

Short answer: Testing frameworks: xUnit, NUnit, MSTest. Mocking libraries: Moq, NSubstitute. IDE support: Visual Studio’s Test Explorer. CI tools: Azure DevOps, GitHub Actions, Jenkins for automated test runs.

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.