C# NUnit

C# NUnit tutorial shows how to do unit testing in C# with NUnit framework. Unit testing is a software testing where individual units of a software are tested.

csharp

Aug 29, 2025

C# NUnit

last modified July 5, 2023

C# NUnit tutorial shows how to do unit testing in C# with NUnit framework.

Unit testing is a software testing where individual units (components) of a software are tested. The purpose of unit testing is to validate that each unit of the software performs as designed. A unit is the smallest testable part of any software.

NUnit is a unit-testing library for all .NET languages. It was inspired by Java’s JUnit. Other unit-testing libraries include XUnit and MSTest.

It is possible to place tests in the same project directory or inside a different directory. We start with a simpler option and place tests in the same project directory. In the end, we show the latter option.

$ dotnet add Microsoft.NET.Test.Sdk $ dotnet new nunit $ dotnet add NUnit3TestAdapter

In order to use NUnit, we need to add these three libraries.

C# NUNit simple example

We start with a simple example.

Arith.cs

namespace Arithmetic;

class Basic { public static Func<int, int, int> add = (a, b) => a + b; public static Func<int, int, int> mul = (a, b) => a * b; public static Func<int, int, int> sub = (a, b) => a - b; public static Func<int, int, int> div = (a, b) => a / b; }

We test simple arithmetic functions.

We put our tests into the tests directory. NUnit automatically discovers our tests.

tests/ArithTest.cs

namespace Testing;

using NUnit.Framework; using Arithmetic;

class ArithTest { [Test] public void SimpleArithmetic() { int r1 = Basic.add(3, 3); Assert.AreEqual(r1, 6);

    int r2 = Basic.sub(3, 3);
    Assert.AreEqual(r2, 0);

    int r3 = Basic.mul(3, 3);
    Assert.AreEqual(r3, 9);

    int r4 = Basic.div(3, 3);
    Assert.AreEqual(r4, 1);
}

}

The test method is annotated with the [Test] attribute. We use assertions to ensure the correct output.

$ dotnet test … Starting test execution, please wait… A total of 1 test files matched the specified pattern.

Passed! - Failed: 0, Passed: 1, Skipped: 0, Total: 1, …

C# NUnit skipping tests

Test methods can be skipped with [Ignore] attribute.

tests/ArithTest.cs

namespace Testing;

using NUnit.Framework; using Arithmetic;

class ArithTest { [Test] public void AddSub() { int r1 = Basic.add(3, 3); Assert.AreEqual(r1, 6);

    int r2 = Basic.sub(3, 3);
    Assert.AreEqual(r2, 0);
}

[Test]
[Ignore("Ignoring")]
public void MulDiv()
{
    int r3 = Basic.mul(3, 3);
    Assert.AreEqual(r3, 9);

    int r4 = Basic.div(3, 3);
    Assert.AreEqual(r4, 1);
}

}

We have two test methods. One of them is skipped using the [Ignore] attribute.

C# NUnit TestCase

With TestCase attribute, we can have parameterized test methods.

tests/ArithTest.cs

namespace Testing;

using NUnit.Framework; using Arithmetic;

class ArithTest { [TestCase(1, 2, 3)] [TestCase(2, 2, 4)] [TestCase(-1, 4, 3)] public void Add(int x, int y, int z) { int r = Basic.add(x, y); Assert.AreEqual(r, z); }

[TestCase(1, 2, -1)]
[TestCase(2, 2, 0)]
[TestCase(3, 2, 1)]
public void Sub(int x, int y, int z)
{
    int r = Basic.sub(x, y);
    Assert.AreEqual(r, z);
}

[TestCase(9, 3, 27)]
[TestCase(3, 3, 9)]
[TestCase(-3, -3, 9)]
public void Mul(int x, int y, int z)
{
    int r = Basic.mul(x, y);
    Assert.AreEqual(r, z);
}

[TestCase(9, 3, 3)]
[TestCase(3, 3, 1)]
[TestCase(8, 2, 4)]
public void Div(int x, int y, int z)
{
    int r = Basic.div(x, y);
    Assert.AreEqual(r, z);
}

}

In this example, we test each method with three sets of values.

C# NUnit TestCaseSource

The [TestCaseSource] attribute allows us to read the data for the parameterized test methods from different sources.

tests/ArithTest.cs

namespace Testing;

using NUnit.Framework; using Arithmetic;

public class ArithTest { [TestCaseSource(nameof(AddCases))] public void Add(int x, int y, int z) { int r = Basic.add(x, y); Assert.AreEqual(r, z); }

[TestCaseSource(nameof(SubCases))]
public void Sub(int x, int y, int z)
{
    int r = Basic.sub(x, y);
    Assert.AreEqual(r, z);
}

[TestCaseSource(nameof(MulCases))]
public void Mul(int x, int y, int z)
{
    int r = Basic.mul(x, y);
    Assert.AreEqual(r, z);
}

[TestCaseSource(nameof(DivCases))]
public void Div(int x, int y, int z)
{
    int r = Basic.div(x, y);
    Assert.AreEqual(r, z);
}

static object[] AddCases =
{
    new object[] { 1, 2, 3 },
    new object[] { 2, 2, 4 },
    new object[] { -1, 4, 3 }
};

static object[] SubCases =
{
    new object[] { 1, 2, -1 },
    new object[] { 2, 2, 0 },
    new object[] { 3, 2, 1 }
};

static object[] MulCases =
{
    new object[] { 9, 3, 27 },
    new object[] { 3, 3, 9 },
    new object[] { -3, -3, 9 }
};

static object[] DivCases =
{
    new object[] { 9, 3, 3 },
    new object[] { 3, 3, 1 },
    new object[] { 8, 2, 4 }
};

}

In this example, the values are placed in arrays.

C# NUnit ExpectedResult

With ExpectedResult, we can simplify our test setup.

tests/ArithTest.cs

namespace Testing;

using NUnit.Framework; using Arithmetic;

class ArithTest { [TestCase(1, 2, ExpectedResult = 3)] [TestCase(2, 2, ExpectedResult = 4)] [TestCase(-1, 4, ExpectedResult = 3)] public int Add(int x, int y) { return Basic.add(x, y); }

[TestCase(1, 2, ExpectedResult = -1)]
[TestCase(2, 2, ExpectedResult = 0)]
[TestCase(3, 2, ExpectedResult = 1)]
public int Sub(int x, int y)
{
    return Basic.sub(x, y);
}

[TestCase(9, 3, ExpectedResult = 27)]
[TestCase(3, 3, ExpectedResult = 9)]
[TestCase(-3, -3, ExpectedResult = 9)]
public int Mul(int x, int y)
{
    return Basic.mul(x, y);
}

[TestCase(9, 3, ExpectedResult = 3)]
[TestCase(3, 3, ExpectedResult = 1)]
[TestCase(8, 2, ExpectedResult = 4)]
public int Div(int x, int y)
{
    return Basic.div(x, y);
}

}

With ExpectedResult, our code is shortened a bit.

Placing tests in separate directory

In the following example, we show how to place tests in a separate directory.

$ mkdir Separate $ cd Separate

We create a new directory.

$ dotnet new sln

We create a new empty solution.

$ mkdir PalindromeService PalindromeService.Tests

Two directories are created.

$ cd PalindromeService $ dotnet new classlib

We create a new library.

PalindromeService\PalindromeService.cs

namespace Palindrome.Services;

using System.Globalization;

public class PalindromeService { public bool IsPalindrome(string word) { IEnumerable<string> GraphemeClusters(string s) { var enumerator = StringInfo.GetTextElementEnumerator(s); while (enumerator.MoveNext()) { yield return (string)enumerator.Current; } }

    var reversed = string.Join("", GraphemeClusters(word).Reverse().ToArray());

    return reversed == word;
}

}

The PalindromeService contains the IsPalindrome method, which determines if a words is a palindrome.

$ cd .. $ dotnet sln add PalindromeService\PalindromeService.csproj

We add the PalindromeService to the solution.

$ cd PalindromeService.Tests $ dotnet add nunit $ dotnet add reference ..\PalindromeService\PalindromeService.csproj

We go to the PalindromeService.Tests directory and add the unit libraries add the reference to the PalindromeService.

PalindromeService.Tests\PalindromeService.Tests.csproj

<PropertyGroup> <TargetFramework>net6.0</TargetFramework> <Nullable>enable</Nullable>

&lt;IsPackable&gt;false&lt;/IsPackable&gt;

</PropertyGroup>

</Project>

This is how the project file looks like.

PalindromeService.Tests\Tests.cs

namespace Palindrome.Services.Tests;

using NUnit.Framework;

public class Tests { private PalindromeService? _palindromeService;

[SetUp]
public void SetUp()
{
    _palindromeService = new PalindromeService();
}

[TestCase("racecar")]
[TestCase("nun")]
[TestCase("level")]
public void IsPalindrome(string word)
{
    var r = _palindromeService!.IsPalindrome(word);
    Assert.AreEqual(r, true);
}

}

We test the IsPalindrome method with three words.

[SetUp] public void SetUp() { _palindromeService = new PalindromeService(); }

The [Setup] attribute is used to provide a common set of functions that are performed just before each test method is called. In our case, we create the PalindromeService.

$ cd .. $ dotnet sln add PalindromeService.Tests\PalindromeService.Tests.csproj

We add the test project to the solution.

$ dotnet test

Finally, we can run the tests.

Source

Unit testing C# with NUnit and .NET Core

In this article we have done unit testing in C# with NUnit library.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

List all C# tutorials.