xUnit is a popular unit testing framework for .NET. It is lightweight, extensible, and well-integrated with .NET testing tools.

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Install xUnit in a .NET Project

To add xUnit to your project, follow these steps:

Using .NET CLI

Run the following command in your terminal:

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

Using NuGet Package Manager

1. Open Visual Studio.
2. Right-click on your test project → Click Manage NuGet Packages.
3. Search for xUnit and install:
   • xunit
   • Microsoft.NET.Test.Sdk
   • xunit.runner.visualstudio

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Create a Test Project

If you don’t have a test project yet, create one:

dotnet new xunit -o MyTests
cd MyTests

This creates a new xUnit test project.

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Writing a Simple xUnit Test

Let’s say we have a simple Calculator class:

Production Code (Calculator.cs)

public class Calculator
{
    public int Add(int a, int b)
    {
        return a + b;
    }

    public int Multiply(int a, int b)
    {
        return a * b;
    }
}

Test Code (CalculatorTests.cs)

using Xunit;

public class CalculatorTests
{
    [Fact]
    public void Add_ShouldReturnCorrectSum()
    {
        // Arrange
        var calculator = new Calculator();

        // Act
        int result = calculator.Add(5, 3);

        // Assert
        Assert.Equal(8, result);
    }

    [Fact]
    public void Multiply_ShouldReturnCorrectProduct()
    {
        // Arrange
        var calculator = new Calculator();

        // Act
        int result = calculator.Multiply(4, 5);

        // Assert
        Assert.Equal(20, result);
    }
}

🔹 Breakdown of [Fact] Attribute:

• [Fact] → Marks a method as a test case in xUnit.
• Assert.Equal(expected, actual) → Checks if the output matches expectations.

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Running Tests

Run the tests using the .NET CLI:

dotnet test

✅ Expected Output:

Test Run Successful.
Total tests: 2
Passed: 2

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Parameterized Tests Using [Theory]

Instead of writing multiple tests manually, we can use [Theory] with [InlineData]:

Parameterized Tests

public class CalculatorTests
{
    private readonly Calculator _calculator = new Calculator();

    [Theory]
    [InlineData(5, 3, 8)]
    [InlineData(10, 2, 12)]
    [InlineData(7, 0, 7)]
    public void Add_ShouldReturnCorrectSum(int a, int b, int expected)
    {
        int result = _calculator.Add(a, b);
        Assert.Equal(expected, result);
    }
}

🔹 Why Use [Theory]?

• It allows running the same test with different inputs.
• Reduces code duplication