feat: auto-configure OpenTelemetry in TestWebApplicationFactory SUT

TUnit.AspNetCore.Core/TUnit.AspNetCore.Core.csproj

@@ -16,10 +16,17 @@
   <ItemGroup>
     <ProjectReference Include="..\TUnit.Core\TUnit.Core.csproj" />
     <ProjectReference Include="..\TUnit.Logging.Microsoft\TUnit.Logging.Microsoft.csproj" />
+    <ProjectReference Include="..\TUnit.OpenTelemetry\TUnit.OpenTelemetry.csproj" />
     <ProjectReference Include="..\TUnit.Core.SourceGenerator\TUnit.Core.SourceGenerator.csproj"
       OutputItemType="Analyzer" ReferenceOutputAssembly="false" />
   </ItemGroup>
 
+  <ItemGroup>
+    <PackageReference Include="OpenTelemetry.Extensions.Hosting" />
+    <PackageReference Include="OpenTelemetry.Instrumentation.AspNetCore" />
+    <PackageReference Include="OpenTelemetry.Instrumentation.Http" />
+  </ItemGroup>
+
   <!-- Framework-specific package versions for Microsoft.AspNetCore.Mvc.Testing -->
   <ItemGroup Condition="'$(TargetFramework)' == 'net8.0'">
     <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="10.0.6" VersionOverride="8.0.0" />

TUnit.AspNetCore.Core/TestWebApplicationFactory.cs

@@ -6,11 +6,13 @@
 using Microsoft.Extensions.DependencyInjection.Extensions;
 using Microsoft.Extensions.Hosting;
 using Microsoft.Extensions.Http;
+using OpenTelemetry.Trace;
 using TUnit.AspNetCore.Extensions;
 using TUnit.AspNetCore.Http;
 using TUnit.AspNetCore.Interception;
 using TUnit.AspNetCore.Logging;
 using TUnit.Core;
+using TUnit.OpenTelemetry;
 
 namespace TUnit.AspNetCore;
 
@@ -50,6 +52,11 @@ public WebApplicationFactory<TEntryPoint> GetIsolatedFactory(
                         services.TryAddEnumerable(
                             ServiceDescriptor.Singleton<IHttpMessageHandlerBuilderFilter, TUnitHttpClientFilter>());
                     }
+
+                    if (options.AutoConfigureOpenTelemetry)
+                    {
+                        AddTUnitOpenTelemetry(services);
+                    }
                 });
 
             if (options.EnableHttpExchangeCapture)
@@ -94,6 +101,24 @@ protected override void ConfigureWebHost(IWebHostBuilder builder)
         });
     }
 
+    /// <summary>
+    /// Adds TUnit's default OpenTelemetry tracing configuration to <paramref name="services"/>:
+    /// the <c>TUnit.AspNetCore.Http</c> activity source, the
+    /// <see cref="TUnitTestCorrelationProcessor"/>, and ASP.NET Core + HttpClient instrumentation.
+    /// Safe to call even if the SUT already registers these — OpenTelemetry de-duplicates them.
+    /// Also safe when combined with the <c>TUnit.OpenTelemetry</c> zero-config package: the
+    /// SUT and test-runner <c>TracerProvider</c>s each carry their own processor, but the
+    /// processor's idempotent <c>OnStart</c> guard prevents duplicate <c>tunit.test.id</c> tags.
+    /// </summary>
+    private static void AddTUnitOpenTelemetry(IServiceCollection services)
+    {
+        services.AddOpenTelemetry().WithTracing(tracing => tracing
+            .AddSource(TUnitActivitySource.AspNetCoreHttpSourceName)
+            .AddProcessor(new TUnitTestCorrelationProcessor())
+            .AddAspNetCoreInstrumentation()
+            .AddHttpClientInstrumentation());
+    }
+
     /// <summary>
     /// Controls whether every registered <see cref="Microsoft.Extensions.Hosting.IHostedService"/>
     /// has its <c>StartAsync</c> dispatched onto a thread-pool worker with a clean

TUnit.AspNetCore.Core/WebApplicationTestOptions.cs

@@ -22,4 +22,22 @@ public record WebApplicationTestOptions
     /// </para>
     /// </summary>
     public bool AutoPropagateHttpClientFactory { get; set; } = true;
+
+    /// <summary>
+    /// Gets or sets a value indicating whether the SUT's <see cref="OpenTelemetry.Trace.TracerProvider"/>
+    /// should be automatically augmented with the TUnit HTTP activity source, the
+    /// <c>TUnitTestCorrelationProcessor</c>, and ASP.NET Core + HttpClient instrumentation.
+    /// Default is <c>true</c>.
+    /// <para>
+    /// When enabled, test spans emitted inside the SUT are tagged with the ambient
+    /// <c>tunit.test.id</c> baggage so they remain queryable per-test in backends like
+    /// Seq or Jaeger, even when third-party libraries break the parent-chain.
+    /// </para>
+    /// <para>
+    /// Set to <c>false</c> to leave the SUT's OpenTelemetry configuration untouched —
+    /// useful if the SUT configures its own processors and you do not want TUnit's
+    /// defaults layered on top.
+    /// </para>
+    /// </summary>
+    public bool AutoConfigureOpenTelemetry { get; set; } = true;
 }

TUnit.AspNetCore.Tests/AutoConfigureOpenTelemetryTests.cs

@@ -0,0 +1,72 @@
+using System.Diagnostics;
+using Microsoft.Extensions.DependencyInjection;
+using OpenTelemetry.Trace;
+using TUnit.AspNetCore;
+using TUnit.Core;
+
+namespace TUnit.AspNetCore.Tests;
+
+/// <summary>
+/// Coverage for thomhurst/TUnit#5594 — <see cref="TestWebApplicationFactory{TEntryPoint}"/>
+/// automatically augments the SUT's <see cref="TracerProvider"/> with TUnit's
+/// correlation processor + ASP.NET Core instrumentation.
+/// </summary>
+/// <remarks>
+/// Serialized against sibling auto-wire tests because <see cref="OpenTelemetry.Sdk"/>
+/// attaches a process-global <see cref="ActivityListener"/> per <c>TracerProvider</c>,
+/// so a parallel factory's correlation processor can tag activities created by another
+/// factory's SUT. Serializing keeps assertions observing only their own factory's wiring.
+/// </remarks>
+[NotInParallel(nameof(AutoConfigureOpenTelemetryTests))]
+public class AutoConfigureOpenTelemetryTests : WebApplicationTest<TestWebAppFactory, Program>
+{
+    private readonly List<Activity> _exported = [];
+
+    protected override void ConfigureTestServices(IServiceCollection services)
+    {
+        services.AddOpenTelemetry().WithTracing(t => t.AddInMemoryExporter(_exported));
+    }
+
+    [Test]
+    public async Task AutoWires_TagsAspNetCoreSpans_WithTestId()
+    {
+        using var client = Factory.CreateClient();
+        var response = await client.GetAsync("/ping");
+        response.EnsureSuccessStatusCode();
+
+        var testId = TestContext.Current!.Id;
+        var taggedSpan = _exported.FirstOrDefault(a => (a.GetTagItem(TUnitActivitySource.TagTestId) as string) == testId);
+        await Assert.That(taggedSpan).IsNotNull();
+    }
+}
+
+[NotInParallel(nameof(AutoConfigureOpenTelemetryTests))]
+public class AutoConfigureOpenTelemetryOptOutTests : WebApplicationTest<TestWebAppFactory, Program>
+{
+    private readonly List<Activity> _exported = [];
+
+    protected override void ConfigureTestOptions(WebApplicationTestOptions options)
+    {
+        options.AutoConfigureOpenTelemetry = false;
+    }
+
+    protected override void ConfigureTestServices(IServiceCollection services)
+    {
+        services.AddOpenTelemetry().WithTracing(t => t
+            .AddAspNetCoreInstrumentation()
+            .AddInMemoryExporter(_exported));
+    }
+
+    [Test]
+    public async Task OptOut_DoesNotTag_AspNetCoreSpans()
+    {
+        using var client = Factory.CreateClient();
+        var response = await client.GetAsync("/ping");
+        response.EnsureSuccessStatusCode();
+
+        foreach (var activity in _exported)
+        {
+            await Assert.That(activity.GetTagItem(TUnitActivitySource.TagTestId)).IsNull();
+        }
+    }
+}

TUnit.AspNetCore.Tests/TUnit.AspNetCore.Tests.csproj

@@ -30,6 +30,10 @@
         <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" />
     </ItemGroup>
 
+    <ItemGroup>
+        <PackageReference Include="OpenTelemetry.Exporter.InMemory" />
+    </ItemGroup>
+
     <Import Project="..\TestProject.targets" />
 
 </Project>

TUnit.Core/TUnitActivitySource.cs

@@ -12,6 +12,13 @@ public static class TUnitActivitySource
     internal const string SourceName = "TUnit";
     internal const string LifecycleSourceName = "TUnit.Lifecycle";
 
+    /// <summary>
+    /// Activity source emitted by TUnit's ASP.NET Core HTTP propagation handlers.
+    /// Registered automatically on the SUT's <see cref="System.Diagnostics.ActivitySource"/>
+    /// listeners by <c>TestWebApplicationFactory</c>.
+    /// </summary>
+    public const string AspNetCoreHttpSourceName = "TUnit.AspNetCore.Http";
+
     /// <summary>W3C baggage HTTP header name.</summary>
     internal const string BaggageHeader = "baggage";
 

TUnit.PublicAPI/Tests.Core_Library_Has_No_API_Changes.DotNet10_0.verified.txt

@@ -1330,6 +1330,7 @@ namespace
     }
     public static class TUnitActivitySource
     {
+        public const string AspNetCoreHttpSourceName = ".Http";
         public const string TagTestId = ".id";
     }
     public class TUnitAttribute :  { }

TUnit.PublicAPI/Tests.Core_Library_Has_No_API_Changes.DotNet8_0.verified.txt

@@ -1330,6 +1330,7 @@ namespace
     }
     public static class TUnitActivitySource
     {
+        public const string AspNetCoreHttpSourceName = ".Http";
         public const string TagTestId = ".id";
     }
     public class TUnitAttribute :  { }

TUnit.PublicAPI/Tests.Core_Library_Has_No_API_Changes.DotNet9_0.verified.txt

@@ -1330,6 +1330,7 @@ namespace
     }
     public static class TUnitActivitySource
     {
+        public const string AspNetCoreHttpSourceName = ".Http";
         public const string TagTestId = ".id";
     }
     public class TUnitAttribute :  { }

docs/docs/examples/aspnet.md

@@ -86,6 +86,7 @@ public class TodoApiTests : TestsBase
 
 - **Client-side tracing**: `CreateClient()` / `CreateDefaultClient()` return an `HttpClient` that propagates `traceparent`, `baggage`, and `X-TUnit-TestId` headers to the SUT.
 - **SUT `IHttpClientFactory` tracing**: Every pipeline built inside the SUT via `AddHttpClient<T>()`, named clients, or typed clients also gets those headers prepended — outbound calls from your app to downstream services correlate with the originating test. Opt out per-test with `WebApplicationTestOptions.AutoPropagateHttpClientFactory = false`.
+- **SUT-side OpenTelemetry**: The SUT's `TracerProvider` is augmented with the `TUnit.AspNetCore.Http` activity source, the `TUnitTestCorrelationProcessor` (stamps the `tunit.test.id` baggage item onto every span as a tag), and ASP.NET Core + HttpClient instrumentation. Spans emitted inside the SUT stay queryable per-test in backends like Jaeger or Seq, even when third-party libraries break the parent-chain. Opt out per-test with `WebApplicationTestOptions.AutoConfigureOpenTelemetry = false`.
 - **Correlated logging**: Server-side `ILogger` output is routed to the test that triggered the request.
 - **Hosted-service context hygiene**: `IHostedService.StartAsync` runs under `ExecutionContext.SuppressFlow()` so background work doesn't inherit the first test's `Activity.Current`.
 

docs/docs/examples/opentelemetry.md

@@ -258,8 +258,15 @@ dotnet add package OpenTelemetry.Exporter.Zipkin
 If you use `TestWebApplicationFactory` or `TracedWebApplicationFactory`, outgoing requests
 automatically propagate the current test trace via W3C `traceparent` and `baggage` headers.
 
-Add `"TUnit.AspNetCore.Http"` as a source only if you also want TUnit's synthetic client spans
-to appear in your exporter. Header propagation works either way.
+The factory also augments the SUT's `TracerProvider` automatically — no manual `services.AddOpenTelemetry().WithTracing(...)` wiring is needed for the basics:
+
+- Registers the `TUnit.AspNetCore.Http` activity source.
+- Adds the `TUnitTestCorrelationProcessor` so spans from libraries with broken parent chains are still tagged with `tunit.test.id`.
+- Adds ASP.NET Core and HttpClient instrumentation.
+
+Your own `WithTracing` callback on the SUT is preserved; TUnit's defaults are layered on top. If you configure your own exporter (OTLP, Jaeger, Zipkin, in-memory), test spans flow straight through it.
+
+Set `WebApplicationTestOptions.AutoConfigureOpenTelemetry = false` per-test to opt out — useful if the SUT owns its own processors and you don't want TUnit's defaults layered on top.
 
 ## Test Context Correlation via Activity Baggage
 

docs/docs/guides/distributed-tracing.md

@@ -150,6 +150,12 @@ protected override void ConfigureTestOptions(WebApplicationTestOptions options)
 }
 ```
 
+### SUT-side OpenTelemetry wiring
+
+`TestWebApplicationFactory<T>` also augments the SUT's `TracerProvider` automatically — the `TUnit.AspNetCore.Http` activity source, the `TUnitTestCorrelationProcessor`, and ASP.NET Core + HttpClient instrumentation are layered on top of whatever `AddOpenTelemetry().WithTracing(...)` wiring the SUT already has. That means spans emitted inside the SUT stay queryable per-test (`tunit.test.id` tag) even when third-party libraries break the parent chain.
+
+Opt out per-test with `WebApplicationTestOptions.AutoConfigureOpenTelemetry = false` when the SUT owns its own processors and you don't want TUnit's defaults layered on top.
+
 ### Raw `HttpClient`
 
 `new HttpClient()` can't be intercepted. Either route through `IHttpClientFactory` or set the `traceparent` header manually.