How do you write a basic test case using xUnit?

Short answer: public class CalculatorTests { [Fact] public void Add_ReturnsSum() { var calculator = new Calculator(); var result = calculator.Add(2, 3); Assert.Equal(5, result); } }

Example code

public class CalculatorTests
{ [Fact] public void Add_ReturnsSum()
{
var calculator = new Calculator();
var result = calculator.Add(2, 3); Assert.Equal(5, result); }
}

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.