Integration TUnit

Example project: A complete working example is available at examples/Example.Api/tests/Example.Api.Tests.Component.TUnit/.

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Overview

This guide walks you through integrating TestTrackingDiagrams with TUnit. After completing this guide, your TUnit tests will automatically generate:

• PlantUML sequence diagrams from HTTP traffic between your service and its dependencies
• HTML reports with embedded diagrams
• YAML specification files

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Prerequisites

• .NET 10.0 SDK or later
• An ASP.NET Core API project to test (your "Service Under Test")
• Basic familiarity with TUnit

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Step 1: Create the Test Project

Create a new console project (TUnit requires OutputType=Exe):

dotnet new console -n MyApi.Tests.Component

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Step 2: Install NuGet Packages

dotnet add package TestTrackingDiagrams.TUnit
dotnet add package TUnit
dotnet add package Microsoft.AspNetCore.Mvc.Testing

Your <ItemGroup> should look like this:

<PropertyGroup>
    <OutputType>Exe</OutputType>
    <IsTestProject>true</IsTestProject>
</PropertyGroup>

<ItemGroup>
    <PackageReference Include="TestTrackingDiagrams.TUnit" Version="2.0.78-beta" />
    <PackageReference Include="TUnit" Version="1.33.0" />
    <PackageReference Include="coverlet.collector" Version="8.0.1">
        <PrivateAssets>all</PrivateAssets>
        <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
    </PackageReference>
</ItemGroup>

Note: TUnit uses Microsoft.Testing.Platform (not Microsoft.NET.Test.Sdk). The TUnit meta package handles the test runner configuration automatically.

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Step 3: Create the Test Run Setup/Teardown

TUnit uses [Before(Assembly)] / [After(Assembly)] hooks for global setup and teardown.

Create Infrastructure/TestRun.cs:

using TestTrackingDiagrams;
using TestTrackingDiagrams.TUnit;
using TUnit.Core;

namespace MyApi.Tests.Component.Infrastructure;

public class TestRun : DiagrammedTestRun
{
    [Before(Assembly)]
    public static void GlobalSetup(AssemblyHookContext context)
    {
        Setup();
        // Optional: start any HTTP fakes here
    }

    [After(Assembly)]
    public static void GlobalTeardown(AssemblyHookContext context)
    {
        EndRunTime = DateTime.UtcNow;

        // Generate reports when the test run ends
        TUnitReportGenerator.CreateStandardReportsWithDiagrams(
            TestContexts,
            StartRunTime,
            EndRunTime,
            new ReportConfigurationOptions
            {
                SpecificationsTitle = "My API Specifications"
            });

        // Optional: dispose HTTP fakes here
    }
}

Key points:

• [Before(Assembly)] and [After(Assembly)] run once at the start and end of the test assembly.
• The AssemblyHookContext parameter is required by TUnit for assembly-level hooks.
• Call Setup() in [Before(Assembly)] — this records the StartRunTime.

---

Step 4: Create the Base Fixture

Create Infrastructure/BaseFixture.cs:

using Microsoft.AspNetCore.Mvc.Testing;
using Microsoft.AspNetCore.TestHost;
using Microsoft.Extensions.DependencyInjection;
using TestTrackingDiagrams.TUnit;

namespace MyApi.Tests.Component.Infrastructure;

public abstract class BaseFixture : DiagrammedComponentTest, IDisposable
{
    private static readonly WebApplicationFactory<Program>? SFactory;
    protected HttpClient Client { get; }

    private const string ServiceUnderTestName = "My API";

    static BaseFixture()
    {
        SFactory = new WebApplicationFactory<Program>().WithWebHostBuilder(builder =>
        {
            builder.ConfigureTestServices(services =>
            {
                services.TrackDependenciesForDiagrams(new TUnitTestTrackingMessageHandlerOptions
                {
                    CallerName = ServiceUnderTestName,
                    PortsToServiceNames =
                    {
                        { 80, ServiceUnderTestName },
                        { 5001, "Downstream Service A" }
                    }
                });
            });
        });
    }

    protected BaseFixture()
    {
        Client = SFactory!.CreateTestTrackingClient(
            new TUnitTestTrackingMessageHandlerOptions
            {
                FixedNameForReceivingService = ServiceUnderTestName
            });
    }

    public void Dispose() => Client.Dispose();
}

Key points:

• DiagrammedComponentTest provides an [After(Test)] hook that automatically enqueues the TestContext for report collection after each test.
• TUnitTestTrackingMessageHandlerOptions uses TUnit's TestContext.Current to resolve the current test's identity.
• TUnit creates a new instance per test by default (no additional configuration needed).

---

Step 5: Write Test Scenarios

Tests are written as regular TUnit [Test] methods. Use the [Endpoint] and [HappyPath] attributes to add metadata for the report.

Scenarios/Cake_Feature.cs:

using TestTrackingDiagrams.TUnit;

namespace MyApi.Tests.Component.Scenarios;

[Endpoint("/cake")]
public partial class Cake_Feature
{
    [Test]
    [HappyPath]
    public async Task Calling_Create_Cake_Endpoint_Returns_Cake()
    {
        await Given_a_valid_post_request_for_the_Cake_endpoint();
        await When_the_request_is_sent_to_the_cake_post_endpoint();
        await Then_the_response_should_be_successful();
    }

    [Test]
    public async Task Calling_Create_Cake_Endpoint_Without_Eggs_Returns_Bad_Request()
    {
        await Given_a_valid_post_request_for_the_Cake_endpoint();
        await But_the_request_body_is_missing_eggs();
        await When_the_request_is_sent_to_the_cake_post_endpoint();
        await Then_the_response_http_status_should_be_bad_request();
    }
}

Scenarios/Cake_Feature.steps.cs:

using System.Net;
using System.Net.Http.Json;
using MyApi.Tests.Component.Infrastructure;

namespace MyApi.Tests.Component.Scenarios;

public partial class Cake_Feature : BaseFixture
{
    private HttpResponseMessage? _response;

    private async Task Given_a_valid_post_request_for_the_Cake_endpoint()
    {
        // Build your request using Client
    }

    private async Task But_the_request_body_is_missing_eggs()
    {
        // Modify request
    }

    private async Task When_the_request_is_sent_to_the_cake_post_endpoint()
    {
        _response = await Client.PostAsJsonAsync("cake", /* request */);
    }

    private async Task Then_the_response_should_be_successful()
    {
        _response!.StatusCode.Should().Be(HttpStatusCode.OK);
    }

    private async Task Then_the_response_http_status_should_be_bad_request()
    {
        _response!.StatusCode.Should().Be(HttpStatusCode.BadRequest);
    }
}

Key points:

• [Endpoint("/cake")] — Sets the endpoint label for this feature group in the report. This attribute maps to TUnit's PropertyAttribute.
• [HappyPath] — Marks a scenario as a happy path (filterable in the HTML report). This maps to TUnit's CategoryAttribute.
• Class and method names are converted from underscore-separated / PascalCase to human-readable format in reports.

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Step 6: Run the Tests

dotnet run

Note: Since TUnit uses Microsoft.Testing.Platform, you run tests with dotnet run instead of dotnet test. However, dotnet test also works if you have the TUnit meta package installed.

After the tests complete, check the bin/Debug/net10.0/Reports/ folder:

File	Description
Specifications.html	HTML specifications with embedded PlantUML sequence diagrams
TestRunReport.html	HTML test run report with diagrams and execution summary
Specifications.yml	YAML specifications

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Architecture Summary

┌─────────────────────────────────┐
│           TestRun               │  ← [Before(Assembly)] / [After(Assembly)]
│     : DiagrammedTestRun         │     Generates reports in [After(Assembly)]
└─────────────────────────────────┘
              │
              ▼
┌─────────────────────────────────┐
│          BaseFixture            │  ← Creates tracked HttpClient
│   : DiagrammedComponentTest     │     Enqueues TestContext via [After(Test)]
│   IDisposable                   │
└─────────────┬───────────────────┘
              │ inherited by
              ▼
┌─────────────────────────────────┐
│  Cake_Feature : BaseFixture     │  ← Your test class with [Test] methods
└─────────────────────────────────┘

---

Using PlantUML Overrides

You can customise diagrams within a test using TrackingDiagramOverride:

using TestTrackingDiagrams.TUnit;

// Insert a delimiter between multiple requests in the diagram
TrackingDiagramOverride.InsertTestDelimiter("Step 1");

// Insert raw PlantUML markup
TrackingDiagramOverride.InsertPlantUml("note over MyApi : Custom note");

// Override the start/end of diagram generation
TrackingDiagramOverride.StartOverride();
TrackingDiagramOverride.EndOverride();

// Explicitly mark the boundary between setup and action phases
TrackingDiagramOverride.StartAction();

Setup separation: When SeparateSetup = true is set on ReportConfigurationOptions, HTTP calls made before StartAction() are wrapped in a visual "Setup" partition in the diagram.

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Customisation Options

ReportConfigurationOptions

Property	Default	Description
SpecificationsTitle	"Specifications"	Title shown at the top of reports
PlantUmlServerBaseUrl	"https://www.plantuml.com/plantuml"	PlantUML server URL
HtmlSpecificationsFileName	"Specifications"	Output filename for specs HTML
HtmlTestRunReportFileName	"TestRunReport"	Output filename for test run HTML
YamlSpecificationsFileName	"Specifications"	Output filename for YAML specs
HtmlSpecificationsCustomStyleSheet	null	Custom CSS appended to specs HTML
ExcludedHeaders	[]	HTTP headers to exclude from diagrams
SeparateSetup	false	When true, HTTP calls made before StartAction() are wrapped in a visual "Setup" partition in the diagram
HighlightSetup	true	When true (and SeparateSetup is enabled), the setup partition is rendered with a background colour

TUnitTestTrackingMessageHandlerOptions

Property	Description
CallerName	Display name for the service making outgoing HTTP calls
FixedNameForReceivingService	Display name for the service receiving requests
PortsToServiceNames	Dictionary mapping port numbers to friendly service names. Unmapped ports appear as localhost_80, localhost_5001, etc.

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Faking Downstream Dependencies (Correctly)

When your SUT calls downstream HTTP services, those calls must flow through TestTrackingMessageHandler to produce proper HTTP-style diagram arrows (with method, status code, headers, body). Do not mock service client interfaces and use MessageTracker to manually log HTTP interactions — this produces event-style (blue) arrows that are misleading.

Recommended approaches:

• In-memory fake APIs — WebApplicationFactory instances that serve canned responses (see Example Project)
• JustEat HttpClient Interception — handler-level interception, chain with TestTrackingMessageHandler
• WireMock.Net — real HTTP server on a random port, map in PortsToServiceNames

See Tracking Dependencies#faking-dependencies-getting-proper-http-tracking for detailed examples of each approach.

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Differences from xUnit v3

If you're migrating from xUnit v3, the key changes are:

Aspect	xUnit v3	TUnit
Package	TestTrackingDiagrams.xUnit3	TestTrackingDiagrams.TUnit
Test runner	xUnit v3 (out-of-process)	TUnit (Microsoft.Testing.Platform)
Test attribute	[Fact] / [Theory]	[Test]
Lifecycle	Collection fixture (ICollectionFixture<T>)	[Before(Assembly)] / [After(Assembly)] hooks
Constructor safety	Guaranteed (fixture init blocks constructors)	Not guaranteed — must self-initialize
Base class	DiagrammedComponentTest (enqueues TestContext via IDisposable.Dispose)	DiagrammedComponentTest (enqueues TestContext via [After(Test)] hook)
Options type	XUnitTestTrackingMessageHandlerOptions	TUnitTestTrackingMessageHandlerOptions
Report generator	XUnitReportGenerator	TUnitReportGenerator
Test SDK	Microsoft.NET.Test.Sdk + xunit.v3	Not needed (TUnit handles this)
Output type	<OutputType>Exe</OutputType>	<OutputType>Exe</OutputType> (handled by TUnit metapackage)
Execution	dotnet test	dotnet run or dotnet test
Namespace	TestTrackingDiagrams.xUnit3	TestTrackingDiagrams.TUnit

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Troubleshooting

Reports folder is empty

• Ensure [After(Assembly)] calls TUnitReportGenerator.CreateStandardReportsWithDiagrams.
• Ensure your test classes inherit from BaseFixture (which inherits from DiagrammedComponentTest).
• Ensure [Before(Assembly)] calls Setup() to record StartRunTime.

Tests are not showing in the report

• Make sure each test class inherits from DiagrammedComponentTest (directly or via BaseFixture). The base class provides an [After(Test)] hook that enqueues the TestContext for report collection.

Empty specifications HTML / YAML

If any test has failed, the specifications files will be blank by design. The TestRunReport.html will still be generated.

Most diagrams are missing / only a few scenarios appear in the report

This is usually caused by TestContext.Current being null when the tracking handler invokes the fetcher. However, this is by design — when the fetcher throws, the handler catches the exception and forwards the request without tracking. The handler instance is not broken; subsequent requests (during actual test execution) will resolve TestContext.Current normally and produce diagrams.

Common causes of genuinely missing diagrams:

• Test classes don't inherit from DiagrammedComponentTest (so TestContext is never enqueued)
• CreateTestTrackingClient isn't used (so the outer handler doesn't attach test identity headers)
• TrackDependenciesForDiagrams isn't called in ConfigureTestServices (so the inner handler doesn't log requests)

Note: Do not replace CurrentTestInfo.Fetcher with a non-throwing variant. The exception is the correct signal — it tells the tracking infrastructure to skip unattributable traffic and allows TestInfoResolver to fall through to TestIdentityScope.Current / GlobalFallback when running on background threads that have an explicit scope set.

[Before(Assembly)] does not block test constructors

Unlike xUnit's ICollectionFixture<T> (which guarantees the fixture is fully initialized before any test constructor runs), TUnit's [Before(Assembly)] runs before test methods but doesn't guarantee execution before test class constructors.

If your [Before(Assembly)] hook starts infrastructure (e.g. in-memory database servers, HTTP fakes) and your BaseFixture static constructor reads that infrastructure, you may hit NullReferenceException on some tests because the constructor ran before the hook finished.

Fix: Don't rely on [Before(Assembly)] for infrastructure that the static factory constructor needs. Instead, initialize it defensively inside the factory creation:

static BaseFixture()
{
    // Initialize infrastructure HERE, not in [Before(Assembly)]
    if (_fakeServer is null)
    {
        _fakeServer = new FakeServer();
        _fakeServer.Start();
    }

    SFactory = new WebApplicationFactory<Program>().WithWebHostBuilder(builder =>
    {
        builder.ConfigureTestServices(services =>
        {
            services.ConfigureWithFakeServer(_fakeServer);
        });
    });
}

Or use a Lazy<WebApplicationFactory<T>> pattern that defers creation until first test access.