using System; using Xunit; public class Calculator { public int Add(int a, int b) { return a + b; } } public class CalculatorTests : ITest { public void Add() { // Arrange Calculator calculator = new Calculator(); int expected = 5; // Act int actual = calculator.Add(2, 3); // Assert Assert.Equal(expected, actual); } }In this example, we have a simple Calculator class with an Add method that takes two integer arguments and returns their sum. We then have a CalculatorTests class that implements the ITest interface and defines a single test case for the Add method. The test case verifies that the Add method correctly adds two integer values and returns the expected result. The Xunit package library is used in this example to perform the actual unit testing and assertion.