feat: cross-process test report aggregation — merged HTML report + single GitHub summary

TUnit.Core/Attributes/TestMetadata/ClassTimelineAttribute.Constants.cs

@@ -0,0 +1,14 @@
+namespace TUnit.Core;
+
+// Constants-only partial, source-linked into TUnit.Reporting.Tool (the linked
+// HtmlReportGenerator reads the property key back out of report sidecars). Keeping the
+// key here — away from the attribute's behaviour and its base types — lets the tool
+// compile just this file, so the engine and the tool can never disagree on the value.
+public sealed partial class ClassTimelineAttribute
+{
+    /// <summary>
+    /// Custom-property key used to round-trip the chosen <see cref="TUnit.Core.Enums.TimelineMode"/> into
+    /// <c>TestDetails.CustomProperties</c> so the HTML reporter can read it back per class.
+    /// </summary>
+    internal const string ClassTimelinePropertyKey = "tunit.report.timeline";
+}

TUnit.Core/Attributes/TestMetadata/ClassTimelineAttribute.cs

@@ -29,7 +29,7 @@ namespace TUnit.Core;
 /// </code>
 /// </example>
 [AttributeUsage(AttributeTargets.Class | AttributeTargets.Assembly)]
-public sealed class ClassTimelineAttribute(TimelineMode mode) : TUnitAttribute, ITestDiscoveryEventReceiver, IScopedAttribute
+public sealed partial class ClassTimelineAttribute(TimelineMode mode) : TUnitAttribute, ITestDiscoveryEventReceiver, IScopedAttribute
 {
     /// <summary>The timeline rendering mode to apply.</summary>
     public TimelineMode Mode { get; } = mode;
@@ -47,9 +47,4 @@ public ValueTask OnTestDiscovered(DiscoveredTestContext context)
         return default;
     }
 
-    /// <summary>
-    /// Custom-property key used to round-trip the chosen <see cref="TimelineMode"/> into
-    /// <c>TestDetails.CustomProperties</c> so the HTML reporter can read it back per class.
-    /// </summary>
-    internal const string ClassTimelinePropertyKey = "tunit.report.timeline";
 }

TUnit.Core/SpanData.cs

@@ -2,7 +2,9 @@
 
 namespace TUnit.Core;
 
-internal sealed class SpanData
+// A record so report merging can rewrite single properties via `with` without a
+// hand-maintained copy that silently drops newly added members.
+internal sealed record SpanData
 {
     [JsonPropertyName("traceId")]
     public required string TraceId { get; init; }

TUnit.Core/TUnitActivitySource.ReportConstants.cs

@@ -0,0 +1,22 @@
+#if NET
+
+namespace TUnit.Core;
+
+// Span/tag constants consumed by the HTML report pipeline (HtmlReportGenerator). They live
+// in this constants-only partial so TUnit.Reporting.Tool can source-link exactly these
+// values without dragging in the ActivitySource statics — which also makes value drift
+// between the engine and the tool impossible. Keep this file free of anything but consts.
+public static partial class TUnitActivitySource
+{
+    // Span names used across the engine and HTML report.
+    internal const string SpanTestSession = "test session";
+    internal const string SpanTestAssembly = "test assembly";
+    internal const string SpanTestSuite = "test suite";
+    internal const string SpanTestCase = "test case";
+    internal const string SpanTestBody = "test body";
+
+    internal const string TagTestClass = "tunit.test.class";
+    internal const string TagTraceScope = "tunit.trace.scope";
+}
+
+#endif

TUnit.Core/TUnitActivitySource.cs

@@ -4,7 +4,7 @@
 
 namespace TUnit.Core;
 
-public static class TUnitActivitySource
+public static partial class TUnitActivitySource
 {
     private static readonly string Version =
         typeof(TUnitActivitySource).Assembly.GetName().Version?.ToString() ?? "0.0.0";
@@ -28,12 +28,8 @@ public static class TUnitActivitySource
     internal static readonly ActivitySource Source = new(SourceName, Version);
     internal static readonly ActivitySource LifecycleSource = new(LifecycleSourceName, Version);
 
-    // Span names used across the engine and HTML report.
-    internal const string SpanTestSession = "test session";
-    internal const string SpanTestAssembly = "test assembly";
-    internal const string SpanTestSuite = "test suite";
-    internal const string SpanTestCase = "test case";
-    internal const string SpanTestBody = "test body";
+    // Span names live in TUnitActivitySource.ReportConstants.cs — a constants-only partial
+    // that TUnit.Reporting.Tool source-links (see that file's header before moving members).
 
     // Tag and baggage keys used across init/dispose spans, HTML report, and cross-boundary correlation.
 
@@ -45,7 +41,6 @@ public static class TUnitActivitySource
     public const string TagTestId = "tunit.test.id";
     internal const string TagSessionId = "tunit.session.id";
     internal const string TagTestFilter = "tunit.filter";
-    internal const string TagTestClass = "tunit.test.class";
     internal const string TagTestMethod = "tunit.test.method";
     internal const string TagTestNodeUid = "tunit.test.node_uid";
     internal const string TagTestCategories = "tunit.test.categories";
@@ -57,7 +52,6 @@ public static class TUnitActivitySource
     internal const string TagTestCaseResultStatus = "test.case.result.status";
     internal const string TagTestRetryAttempt = "tunit.test.retry_attempt";
     internal const string TagTestSkipReason = "tunit.test.skip_reason";
-    internal const string TagTraceScope = "tunit.trace.scope";
 
     /// <summary>
     /// Returns a human-readable type name suitable for span labels.

TUnit.Engine/Configuration/EnvironmentConstants.cs

@@ -12,6 +12,17 @@ internal static class EnvironmentConstants
     // TUnit-specific: how long (in days) the auto-uploaded HTML report artifact is kept
     public const string ArtifactRetentionDays = "TUNIT_ARTIFACT_RETENTION_DAYS";
 
+    // TUnit-specific: cross-process report aggregation (issue #4522).
+    // ON by default wherever a shared directory is resolvable (GitHub Actions, or explicit
+    // TUNIT_AGGREGATE_DIR). Values: off/false/0/no/disabled/none = disable;
+    // defer = persist sidecars + merged HTML only (final summary via `tunit-report merge`);
+    // anything else (or unset) = cooperative merge.
+    public const string AggregateReports = "TUNIT_AGGREGATE_REPORTS";
+    // Shared directory for sidecars/merged outputs; auto-derived on GitHub Actions when unset.
+    public const string AggregateDirectory = "TUNIT_AGGREGATE_DIR";
+    // Opts out of the machine-readable JSON sidecar written next to the HTML report.
+    public const string DisableJsonReport = "TUNIT_DISABLE_JSON_REPORT";
+
     // TUnit-specific: Execution
     public const string ExecutionMode = "TUNIT_EXECUTION_MODE";
     public const string MaxParallelTests = "TUNIT_MAX_PARALLEL_TESTS";
@@ -44,6 +55,11 @@ internal static class EnvironmentConstants
     // Used to clamp TUNIT_ARTIFACT_RETENTION_DAYS so the API does not reject the request.
     public const string GitHubRetentionDays = "GITHUB_RETENTION_DAYS";
 
+    // GitHub Actions context (for report aggregation scoping)
+    public const string RunnerTemp = "RUNNER_TEMP";
+    public const string GitHubRunAttempt = "GITHUB_RUN_ATTEMPT";
+    public const string GitHubJob = "GITHUB_JOB";
+
     // GitHub Actions context (for CI metadata in reports)
     public const string GitHubSha = "GITHUB_SHA";
     public const string GitHubRef = "GITHUB_REF";