NUnit Testing

Diagnostic Output Budget

Keep native test progress and ANSI visible; use the detected runner's supported flags (--progress on --ansi on for MTP/TUnit), not MTP switches on VSTest. Keep console logs at Warning or higher and one concise final summary. Do not replay progress redraws, successful-test output, or Information/Debug/Trace logs into model context. On failure/crash, show only the failing test/resource, root error, and relevant stack frames; deduplicate and cap each diagnostic response at 80 lines / 8 KiB. Never dump entire console/host/browser logs, HTML, TRX, or crash artifacts. Keep necessary artifacts size-bounded outside context, link them, and inspect exact bounded excerpts. Preserve the runner exit code through capture/filtering; disclose truncation. Silence alone does not establish a hang.

Trigger On

• writing or reviewing NUnit tests
• using [Test], [TestCase], [TestFixture], [SetUp], [TearDown] attributes
• configuring NUnit3TestAdapter or NUnit.Analyzers
• migrating between NUnit versions
• integrating NUnit with CI pipelines

Documentation

• NUnit Documentation
• NUnit GitHub
• NUnit3TestAdapter
• NUnit Analyzers

Workflow

1. Detect whether the project uses NUnit 3.x or 4.x and which runner path is active: VSTest, Microsoft.Testing.Platform, IDE runner, or CI wrapper.
2. Keep test fixtures small, prefer focused assertions with Assert.That, and use TestCase or TestCaseSource only when parameterization improves signal.
3. Add NUnit3TestAdapter, Microsoft.NET.Test.Sdk, and NUnit.Analyzers when CLI discovery or analyzer coverage is missing.
4. Validate with the repo's real test command before changing assertion style or lifecycle hooks.

References

• patterns.md — Test patterns, assertions, parameterized tests, lifecycle
• anti-patterns.md — Common NUnit mistakes and fixes

Package Selection

Package	Purpose
NUnit	Core testing framework
NUnit3TestAdapter	VSTest adapter for dotnet test
NUnit.Analyzers	Roslyn analyzers for NUnit best practices
Microsoft.NET.Test.Sdk	Required for test discovery

Project Setup

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net8.0</TargetFramework>
    <IsPackable>false</IsPackable>
    <IsTestProject>true</IsTestProject>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.*" />
    <PackageReference Include="NUnit" Version="4.*" />
    <PackageReference Include="NUnit3TestAdapter" Version="4.*" />
    <PackageReference Include="NUnit.Analyzers" Version="4.*">
      <PrivateAssets>all</PrivateAssets>
      <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
    </PackageReference>
  </ItemGroup>
</Project>

Test Patterns

Basic Test Structure

[TestFixture]
public class CalculatorTests
{
    private Calculator _calculator;

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

    [TearDown]
    public void TearDown()
    {
        _calculator?.Dispose();
    }

    [Test]
    public void Add_TwoPositiveNumbers_ReturnsSum()
    {
        var result = _calculator.Add(2, 3);

        Assert.That(result, Is.EqualTo(5));
    }

    [Test]
    public void Divide_ByZero_ThrowsException()
    {
        Assert.Throws<DivideByZeroException>(() => _calculator.Divide(10, 0));
    }
}

Parameterized Tests with TestCase

[TestFixture]
public class ValidationTests
{
    [TestCase("", false)]
    [TestCase("a", false)]
    [TestCase("ab", false)]
    [TestCase("abc", true)]
    [TestCase("valid@email.com", true)]
    public void IsValid_VariousInputs_ReturnsExpected(string input, bool expected)
    {
        var result = Validator.IsValid(input);

        Assert.That(result, Is.EqualTo(expected));
    }

    [TestCase(1, 2, ExpectedResult = 3)]
    [TestCase(-1, 1, ExpectedResult = 0)]
    [TestCase(100, 200, ExpectedResult = 300)]
    public int Add_TestCases_ReturnsExpectedResult(int a, int b)
    {
        return _calculator.Add(a, b);
    }
}

TestCaseSource for Complex Data

[TestFixture]
public class OrderTests
{
    private static IEnumerable<TestCaseData> OrderTestCases()
    {
        yield return new TestCaseData(
            new Order { Items = new[] { new Item { Price = 10 }, new Item { Price = 20 } } },
            30m
        ).SetName("TwoItems_CalculatesTotal");

        yield return new TestCaseData(
            new Order { Items = Array.Empty<Item>() },
            0m
        ).SetName("EmptyOrder_ReturnsZero");

        yield return new TestCaseData(
            new Order { Items = new[] { new Item { Price = 100 } }, DiscountPercent = 10 },
            90m
        ).SetName("WithDiscount_AppliesDiscount");
    }

    [TestCaseSource(nameof(OrderTestCases))]
    public void CalculateTotal_VariousOrders_ReturnsExpected(Order order, decimal expected)
    {
        var result = order.CalculateTotal();

        Assert.That(result, Is.EqualTo(expected));
    }
}

Constraint-Based Assertions

[Test]
public void AssertionExamples()
{
    // Equality
    Assert.That(actual, Is.EqualTo(expected));
    Assert.That(actual, Is.Not.EqualTo(other));

    // Comparison
    Assert.That(value, Is.GreaterThan(5));
    Assert.That(value, Is.LessThanOrEqualTo(10));
    Assert.That(value, Is.InRange(1, 100));

    // String
    Assert.That(str, Does.StartWith("Hello"));
    Assert.That(str, Does.Contain("world"));
    Assert.That(str, Does.Match(@"\d{3}-\d{4}"));
    Assert.That(str, Is.EqualTo("HELLO").IgnoreCase);

    // Collection
    Assert.That(list, Has.Count.EqualTo(5));
    Assert.That(list, Contains.Item("expected"));
    Assert.That(list, Is.All.GreaterThan(0));
    Assert.That(list, Is.Unique);
    Assert.That(list, Is.Ordered);
    Assert.That(list, Has.Exactly(3).Items.GreaterThan(10));

    // Type
    Assert.That(obj, Is.InstanceOf<MyClass>());
    Assert.That(obj, Is.AssignableTo<IMyInterface>());

    // Null
    Assert.That(obj, Is.Null);
    Assert.That(obj, Is.Not.Null);

    // Boolean
    Assert.That(condition, Is.True);
    Assert.That(condition, Is.False);

    // Exception
    Assert.That(() => DoSomething(), Throws.TypeOf<InvalidOperationException>());
    Assert.That(() => DoSomething(), Throws.Exception.With.Message.Contains("error"));

    // Async
    Assert.That(async () => await DoAsync(), Throws.Nothing);
}

Async Test Support

[TestFixture]
public class AsyncServiceTests
{
    private IAsyncService _service;

    [SetUp]
    public void SetUp()
    {
        _service = new AsyncService();
    }

    [Test]
    public async Task GetDataAsync_ValidId_ReturnsData()
    {
        var result = await _service.GetDataAsync(1);

        Assert.That(result, Is.Not.Null);
        Assert.That(result.Id, Is.EqualTo(1));
    }

    [Test]
    public void GetDataAsync_InvalidId_ThrowsException()
    {
        Assert.ThrowsAsync<NotFoundException>(
            async () => await _service.GetDataAsync(-1));
    }

    [Test]
    public async Task ProcessAsync_CancellationRequested_ThrowsOperationCanceled()
    {
        using var cts = new CancellationTokenSource();
        cts.Cancel();

        Assert.ThrowsAsync<OperationCanceledException>(
            async () => await _service.ProcessAsync(cts.Token));
    }
}

OneTimeSetUp and OneTimeTearDown

[TestFixture]
public class IntegrationTests
{
    private static TestServer _server;
    private HttpClient _client;

    [OneTimeSetUp]
    public void OneTimeSetUp()
    {
        // Runs once before all tests in fixture
        _server = new TestServer(new WebHostBuilder().UseStartup<Startup>());
    }

    [OneTimeTearDown]
    public void OneTimeTearDown()
    {
        // Runs once after all tests in fixture
        _server?.Dispose();
    }

    [SetUp]
    public void SetUp()
    {
        // Runs before each test
        _client = _server.CreateClient();
    }

    [TearDown]
    public void TearDown()
    {
        // Runs after each test
        _client?.Dispose();
    }

    [Test]
    public async Task GetEndpoint_ReturnsSuccess()
    {
        var response = await _client.GetAsync("/api/data");
        Assert.That(response.IsSuccessStatusCode, Is.True);
    }
}

Categories and Filtering

[TestFixture]
[Category("Integration")]
public class DatabaseTests
{
    [Test]
    [Category("Slow")]
    public void SlowDatabaseTest() { }

    [Test]
    [Category("Fast")]
    public void FastDatabaseTest() { }
}

// Run specific categories:
// dotnet test --filter "Category=Fast"
// dotnet test --filter "Category!=Slow"

Anti-Patterns to Avoid

Anti-Pattern	Why It's Bad	Better Approach
Multiple asserts without clear purpose	Hard to identify which assertion failed	One logical assertion per test or use Assert.Multiple
Test interdependence	Tests fail unpredictably	Each test should be independent
Hardcoded test data	Brittle tests	Use TestCase or TestCaseSource
Testing implementation details	Breaks on refactoring	Test behavior, not internals
Missing [SetUp]/[TearDown] cleanup	Resource leaks	Always clean up resources
Classic Assert syntax	Less readable	Use constraint model (Assert.That)

Running Tests

# Run all tests
dotnet test

# VSTest: concise console results; MTP uses its own progress/ANSI flags
dotnet test --logger "console;verbosity=minimal"

# Filter by name
dotnet test --filter "FullyQualifiedName~CalculatorTests"

# Filter by category
dotnet test --filter "Category=Unit"

# Run in parallel
dotnet test -- NUnit.NumberOfTestWorkers=4

Deliver

• NUnit tests following the Arrange-Act-Assert pattern
• Parameterized tests with [TestCase] and [TestCaseSource]
• Constraint-based assertions with Assert.That
• Proper test lifecycle management

Validate

• Tests are independent and isolated
• No hardcoded test data where parameterization is appropriate
• Async tests use async Task not async void
• Resources are properly disposed in [TearDown] or [OneTimeTearDown]
• NUnit.Analyzers enabled to catch common issues