Describe a situation where unit testing saved you from a critical bug.

Short answer: In one project, a unit test caught a null reference exception caused by missing initialization. This early detection prevented the bug from reaching production, saving hours of debugging and user impact.

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.