nunit

NUnit

Ported from JUnit, NUnit is one of the oldest and most feature-rich frameworks for .NET. Ideally suited for complex test setups and legacy migrations.

When to Use

• C# and .NET Testing: A mature, feature-rich testing framework widely used across enterprise .NET applications.
• Parameterized & Combinatorial Testing: Generating test matrices effortlessly with [TestCase] and [Combinatorial].
• Constraint-Based Assertions: Writing expressive assertions using the Assert.That() syntax.
• ASP.NET Core & Unity Game Testing: Testing web APIs, microservices, and Unity game scripts.

Quick Start

using NUnit.Framework;

[TestFixture] public class Tests { [SetUp] public void Setup() { }

[Test]
public void Test1()
{
    Assert.Pass();
}

[TestCase(1, 2, 3)]
[TestCase(2, 2, 4)]
public void TestAdd(int a, int b, int expected)
{
   Assert.AreEqual(expected, a + b);
}

}

## Core Concepts

### Constraint-Based Assertion Model

NUnit emphasizes fluent constraint assertions over legacy multiple-assert methods:

```csharp
using NUnit.Framework;

[TestFixture]
public class AccountTests
{
    [Test]
    public void TestDepositIncreasesBalance()
    {
        var account = new Account(100);
        account.Deposit(50);

        Assert.That(account.Balance, Is.EqualTo(150));
        Assert.That(account.Transactions, Has.Count.EqualTo(1));
        Assert.That(account.Owner, Does.StartWith("Jane"));
    }
}

Parameterized Test Cases ([TestCase])

Passes inline parameters to test multiple input/output permutations:

[TestCase(10, 20, 30)]
[TestCase(-5, 5, 0)]
[TestCase(0, 0, 0)]
public void Add_ReturnsCorrectSum(int a, int b, int expected)
{
    var calculator = new Calculator();
    Assert.That(calculator.Add(a, b), Is.EqualTo(expected));
}

Multiple Assertions Block (Assert.Multiple)

Executes all assertions in a block, reporting all failures rather than terminating on the first:

[Test]
public void ValidateUserRecord()
{
    var user = GetUser();
    Assert.Multiple(() =>
    {
        Assert.That(user.FirstName, Is.EqualTo("Jane"));
        Assert.That(user.LastName, Is.EqualTo("Doe"));
        Assert.That(user.IsActive, Is.True);
    });
}

Common Patterns

Parameterized Test Fixture with Setup

Problem: Redundant boilerplate when testing multiple implementations of the same interface.

Solution: Use [TestCase] with typed expectations:

using NUnit.Framework;

[TestFixture]
public class CalculatorTests
{
    private Calculator _calculator;

    [SetUp]
    public void SetUp()
    {
        _calculator = new Calculator();
    }

    [TestCase(5, 3, 8)]
    [TestCase(-1, 1, 0)]
    [TestCase(0, 0, 0)]
    public void Add_ReturnsExpectedSum(int a, int b, int expected)
    {
        int result = _calculator.Add(a, b);
        Assert.That(result, Is.EqualTo(expected));
    }
}

Best Practices

Do:

• Adopt Assert.Multiple: Run all field assertions on complex objects to view full failure contexts simultaneously.
• Use Assert.That Exclusively: Modern NUnit deprecates legacy Assert.AreEqual() in favor of the constraint model.
• Enable Parallel Execution: Add [assembly: Parallelizable(ParallelScope.Fixtures)] to accelerate test execution.
• Pair with FluentAssertions: Combine with FluentAssertions library for enhanced assertion readability.

Don't:

• Use [SetUp] for slow integration setup: Use [OneTimeSetUp] for database connections shared across the fixture.
• Leave static shared state unreset: Ensure parallelizable test fixtures do not mutate static state.
• Write huge monolithic test methods: Keep test methods focused on single business behaviors.

Troubleshooting

Error	Cause	Solution
No test is available in ... Make sure test project has reference	Missing NUnit3TestAdapter NuGet package in test project.	Install NUnit3TestAdapter and Microsoft.NET.Test.Sdk.
AssertionException: Expected: ... But was: ...	Calculation result does not match expectation.	Check logic and verify constraints using fluent Assert.That(actual, Is.EqualTo(expected)).
System.NullReferenceException in SetUp	Accessing uninitialized fixture field in test execution.	Ensure initialization code is in a [SetUp] method, not in standard constructor.

References

• NUnit Documentation