How do You Use xUnit for Testing in .NET?

xUnit is a popular, open-source testing framework for .NET, widely used for unit testing in .NET Core and .NET 5/6/7+ applications. It is designed to be extensible, clean, and strongly aligned with modern .NET patterns and tools.

What Is xUnit?

• xUnit is part of the “xUnit family” of testing frameworks (along with NUnit, MSTest).
• It was created by the same people who developed NUnit.
• Fully compatible with .NET Core and .NET Standard.
• Preferred by Microsoft for .NET Core projects.

 Installing xUnit in a .NET Project

1. Open your .csproj-based solution.
2. Create a test project (if not already created):

dotnet new xunit -n MyApp.Tests
cd MyApp.Tests

Add reference to your main project:

dotnet add reference ../MyApp/MyApp.csproj

Install xunit, xunit.runner.visualstudio, and Microsoft.NET.Test.Sdk:

dotnet add package xunit
dotnet add package xunit.runner.visualstudio
dotnet add package Microsoft.NET.Test.Sdk

Writing a Simple xUnit Test

Suppose you have the following method in your main project:

// MyApp/Services/Calculator.cs
namespace MyApp.Services
{ public class Calculator { public int Add(int a, int b) => a + b; public int Divide(int a, int b) => a / b; }
}

Example Test Class:

// MyApp.Tests/CalculatorTests.cs
using MyApp.Services;
using Xunit;
namespace MyApp.Tests
{ public class CalculatorTests { [Fact] // A single unit test public void Add_ReturnsCorrectSum() { var calc = new Calculator(); var result = calc.Add(2, 3); Assert.Equal(5, result); } [Fact] public void Divide_ByZero_ThrowsDivideByZeroException() { var calc = new Calculator(); Assert.Throws<DivideByZeroException>(() => calc.Divide(10, 0)); } }
}

Using [Theory] and [InlineData] for Parameterized Tests

public class CalculatorTests
{ [Theory] [InlineData(1, 2, 3)] [InlineData(5, 10, 15)] [InlineData(-1, -1, -2)] public void Add_ReturnsExpectedResult(int a, int b, int expected) { var calc = new Calculator(); var result = calc.Add(a, b); Assert.Equal(expected, result); }
}

Assertions in xUnit

xUnit provides various assertion methods:

Running Tests

From terminal:

dotnet test

From Visual Studio:

• Open Test Explorer (Test > Test Explorer)
• Click Run All

Best Practices

• Keep your unit tests isolated and repeatable.
• Name test methods clearly: MethodName_StateUnderTest_ExpectedBehavior()
• Use Theory when testing multiple input cases.
• Mock external dependencies (e.g., using Moq).
• Keep tests in a separate test project.