How do you test private methods or classes?

Short answer: Best practice is to test private methods indirectly through public methods. If needed, internal methods can be exposed to test projects using InternalsVisibleTo attribute. Reflection can be used but is generally discouraged as it breaks encapsulation.

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.