Replace Report.ExpandClassTimeline with [ClassTimeline] attribute

TUnit.Core/Attributes/TestMetadata/ClassTimelineAttribute.cs

@@ -0,0 +1,55 @@
+using TUnit.Core.Enums;
+using TUnit.Core.Interfaces;
+
+namespace TUnit.Core;
+
+/// <summary>
+/// Opts a test class (or every class in an assembly) into a specific HTML-report
+/// class-timeline rendering mode. Class-level usage wins over assembly-level usage.
+/// </summary>
+/// <remarks>
+/// <para>
+/// Useful for BDD-style chains of <see cref="DependsOnAttribute"/> tests where seeing the
+/// whole flow on one timeline matters, without making every class noisier in the report.
+/// </para>
+/// </remarks>
+/// <example>
+/// <code>
+/// [ClassTimeline(TimelineMode.FullExecution)]
+/// public class OrderProcessingFlow
+/// {
+///     [Test] public Task SetupWiremock() => Task.CompletedTask;
+///
+///     [Test, DependsOn(nameof(SetupWiremock))]
+///     public Task SendMessage() => Task.CompletedTask;
+///
+///     [Test, DependsOn(nameof(SendMessage))]
+///     public Task VerifyWiremockWasCalled() => Task.CompletedTask;
+/// }
+/// </code>
+/// </example>
+[AttributeUsage(AttributeTargets.Class | AttributeTargets.Assembly)]
+public sealed class ClassTimelineAttribute(TimelineMode mode) : TUnitAttribute, ITestDiscoveryEventReceiver, IScopedAttribute
+{
+    /// <summary>The timeline rendering mode to apply.</summary>
+    public TimelineMode Mode { get; } = mode;
+
+    /// <inheritdoc />
+    public int Order => 0;
+
+    /// <inheritdoc />
+    public Type ScopeType => typeof(ClassTimelineAttribute);
+
+    /// <inheritdoc />
+    public ValueTask OnTestDiscovered(DiscoveredTestContext context)
+    {
+        context.AddProperty(ClassTimelinePropertyKey, Mode.ToString());
+        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/Enums/TimelineMode.cs

@@ -0,0 +1,22 @@
+namespace TUnit.Core.Enums;
+
+/// <summary>
+/// Controls how the HTML report renders the class-level execution timeline. Used by
+/// <see cref="ClassTimelineAttribute"/>.
+/// </summary>
+public enum TimelineMode
+{
+    /// <summary>
+    /// Drop test-case spans and their full subtrees from the class timeline, leaving only
+    /// class-level infrastructure (suite, init/dispose). Same as the implicit default for
+    /// classes without a <see cref="ClassTimelineAttribute"/>.
+    /// </summary>
+    Collapsed = 0,
+
+    /// <summary>
+    /// Render the union of every test-case span and its non-<c>test body</c> children on
+    /// the class timeline. Surfaces multi-step <c>[DependsOn]</c> / BDD-style flows
+    /// end-to-end at the class level.
+    /// </summary>
+    FullExecution = 1,
+}

TUnit.Core/Settings/TUnitSettings.cs

@@ -38,9 +38,4 @@ internal TUnitSettings() { }
     /// Controls test run behavior.
     /// </summary>
     public ExecutionSettings Execution { get; } = new();
-
-    /// <summary>
-    /// Controls HTML report rendering.
-    /// </summary>
-    public ReportSettings Report { get; } = new();
 }

TUnit.Engine.Tests/HtmlReporterTests.cs

@@ -7,6 +7,7 @@
 using Microsoft.Testing.Platform.TestHost;
 using Shouldly;
 using TUnit.Core;
+using TUnit.Core.Enums;
 using TUnit.Engine.Reporters.Html;
 
 namespace TUnit.Engine.Tests;
@@ -207,6 +208,60 @@ public async Task PublishArtifactAsync_Publishes_With_Correct_SessionUid()
         }
     }
 
+    [Test]
+    public void ClassTimelineAttribute_Exposes_Mode_And_ScopeType()
+    {
+        var full = new ClassTimelineAttribute(TimelineMode.FullExecution);
+        full.Mode.ShouldBe(TimelineMode.FullExecution);
+        full.ScopeType.ShouldBe(typeof(ClassTimelineAttribute));
+
+        var collapsed = new ClassTimelineAttribute(TimelineMode.Collapsed);
+        collapsed.Mode.ShouldBe(TimelineMode.Collapsed);
+    }
+
+    [Test]
+    public void GenerateHtml_RoundTrips_ClassTimeline_CustomProperty_OnTest()
+    {
+        // The JS reads group.tests[0].customProperties for tunit.report.timeline; this
+        // pins the contract that the property survives serialisation into the embedded JSON.
+        var html = HtmlReportGenerator.GenerateHtml(new ReportData
+        {
+            AssemblyName = "Tests",
+            MachineName = "machine",
+            Timestamp = "2026-05-07T09:26:24.0000000Z",
+            TUnitVersion = "1.0.0",
+            OperatingSystem = "Linux",
+            RuntimeVersion = ".NET 10.0",
+            TotalDurationMs = 0,
+            Summary = new ReportSummary(),
+            Groups =
+            [
+                new ReportTestGroup
+                {
+                    ClassName = "BddFlow",
+                    Namespace = "Sample",
+                    Summary = new ReportSummary(),
+                    Tests =
+                    [
+                        new ReportTestResult
+                        {
+                            Id = "t1", DisplayName = "t1", MethodName = "t1",
+                            ClassName = "BddFlow", Status = "passed",
+                            CustomProperties =
+                            [
+                                new ReportKeyValue { Key = ClassTimelineAttribute.ClassTimelinePropertyKey, Value = nameof(TimelineMode.FullExecution) }
+                            ],
+                        },
+                    ],
+                },
+            ],
+        });
+
+        var embedded = ExtractEmbeddedReportJson(html);
+        embedded.ShouldContain("\"key\":\"tunit.report.timeline\"");
+        embedded.ShouldContain("\"value\":\"FullExecution\"");
+    }
+
     private static ReportTestResult CreateTestResultWithStartTime(string displayName, string? startTime) => new()
     {
         Id = displayName,

TUnit.Engine/Reporters/Html/HtmlReportDataModel.cs

@@ -49,9 +49,6 @@ internal sealed class ReportData
 
     [JsonPropertyName("repositorySlug")]
     public string? RepositorySlug { get; init; }
-
-    [JsonPropertyName("expandClassTimeline")]
-    public bool ExpandClassTimeline { get; init; }
 }
 
 internal sealed class ReportSummary

TUnit.Engine/Reporters/Html/HtmlReportGenerator.cs

@@ -1611,9 +1611,10 @@ function walk(sid) {
 }
 
 // 'test body' must match TUnitActivitySource.SpanTestBody in C#.
-// Used by renderTrace (per-test view, always) and by renderSuiteTrace only when
-// data.expandClassTimeline is true. The default class-timeline branch excludes
-// test-case spans + their entire subtrees, so no test-body span survives to collapse.
+// Used by renderTrace (per-test view, always) and by renderSuiteTrace only when the
+// class opts in via [ClassTimeline(TimelineMode.FullExecution)]. The default
+// class-timeline branch excludes test-case spans + their entire subtrees, so no
+// test-body span survives to collapse.
 function collapseTestBodySpans(spans) {
     if (!spans || !spans.length) return [];
     const byId = {};
@@ -1736,14 +1737,25 @@ function renderClassSummary(g, ft) {
     return h;
 }
 
-function renderSuiteTrace(className) {
+// Per-class opt-in: [ClassTimeline(TimelineMode.FullExecution)] writes 'tunit.report.timeline'
+// onto every test in the class via DiscoveredTestContext.AddProperty.
+// Key/value strings must match ClassTimelineAttribute.ClassTimelinePropertyKey
+// and nameof(TimelineMode.FullExecution) in C#.
+function isClassTimelineFullExecution(group) {
+    const test = group.tests && group.tests[0];
+    if (!test || !test.customProperties) return false;
+    return test.customProperties.some(p => p.key === 'tunit.report.timeline' && p.value === 'FullExecution');
+}
+
+function renderSuiteTrace(group) {
+    const className = group.className;
     const suite = suiteSpanByClass[className];
     if (!suite) return '';
     const allSpans = spansByTrace[suite.traceId];
     if (!allSpans) return '';
     const all = getDescendants(allSpans, suite.spanId);
     let filtered;
-    if (data.expandClassTimeline) {
+    if (isClassTimelineFullExecution(group)) {
         // BDD/DependsOn mode: include test-case spans and their non-'test body' children
         // so multi-step flows are visible at the class level.
         filtered = collapseTestBodySpans(all);
@@ -1901,7 +1913,7 @@ function render() {
         html += '<div class="grp-body"><div class="grp-body-inner"><div class="grp-body-pad">';
         if (groupMode === 'class') {
             html += renderClassSummary(g, ft);
-            html += renderSuiteTrace(g.className);
+            html += renderSuiteTrace(g);
         }
         ft.forEach((t,ti)=>{
             html += '<div class="t-row" id="test-'+t.id+'" data-gi="'+gi+'" data-ti="'+ti+'" data-tid="'+t.id+'" style="--row-idx:'+Math.min(ti,7)+'">';

TUnit.Engine/Reporters/Html/HtmlReporter.cs

@@ -12,7 +12,6 @@
 using Microsoft.Testing.Platform.Services;
 using Microsoft.Testing.Platform.TestHost;
 using TUnit.Core;
-using TUnit.Core.Settings;
 using TUnit.Engine.Configuration;
 using TUnit.Engine.Constants;
 using TUnit.Engine.Exceptions;
@@ -379,7 +378,6 @@ private ReportData BuildReportData()
             Branch = branch,
             PullRequestNumber = prNumber,
             RepositorySlug = repoSlug,
-            ExpandClassTimeline = TUnitSettings.Default.Report.ExpandClassTimeline,
         };
     }
 

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

@@ -381,6 +381,15 @@ namespace
         public static .ClassMetadata GetOrAdd(string name, <.ClassMetadata> factory) { }
         public static .ClassMetadata GetOrAdd(string name, .ClassMetadata value) { }
     }
+    [(.Assembly | .Class)]
+    public sealed class ClassTimelineAttribute : .TUnitAttribute, .IScopedAttribute, ., .
+    {
+        public ClassTimelineAttribute(. mode) { }
+        public . Mode { get; }
+        public int Order { get; }
+        public  ScopeType { get; }
+        public . OnTestDiscovered(.DiscoveredTestContext context) { }
+    }
     [(.Class | .Method)]
     public sealed class CombinedDataSourcesAttribute : .AsyncUntypedDataSourceGeneratorAttribute
     {
@@ -1934,6 +1943,11 @@ namespace .Enums
         Generated = 2,
         Derived = 3,
     }
+    public enum TimelineMode
+    {
+        Collapsed = 0,
+        FullExecution = 1,
+    }
 }
 namespace .Events
 {
@@ -2975,16 +2989,11 @@ namespace .Settings
     {
         public int? MaximumParallelTests { get; set; }
     }
-    public sealed class ReportSettings
-    {
-        public bool ExpandClassTimeline { get; set; }
-    }
     public sealed class TUnitSettings
     {
         public . Display { get; }
         public . Execution { get; }
         public . Parallelism { get; }
-        public . Report { get; }
         public . Timeouts { get; }
     }
     public sealed class TimeoutSettings

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

@@ -381,6 +381,15 @@ namespace
         public static .ClassMetadata GetOrAdd(string name, <.ClassMetadata> factory) { }
         public static .ClassMetadata GetOrAdd(string name, .ClassMetadata value) { }
     }
+    [(.Assembly | .Class)]
+    public sealed class ClassTimelineAttribute : .TUnitAttribute, .IScopedAttribute, ., .
+    {
+        public ClassTimelineAttribute(. mode) { }
+        public . Mode { get; }
+        public int Order { get; }
+        public  ScopeType { get; }
+        public . OnTestDiscovered(.DiscoveredTestContext context) { }
+    }
     [(.Class | .Method)]
     public sealed class CombinedDataSourcesAttribute : .AsyncUntypedDataSourceGeneratorAttribute
     {
@@ -1934,6 +1943,11 @@ namespace .Enums
         Generated = 2,
         Derived = 3,
     }
+    public enum TimelineMode
+    {
+        Collapsed = 0,
+        FullExecution = 1,
+    }
 }
 namespace .Events
 {
@@ -2975,16 +2989,11 @@ namespace .Settings
     {
         public int? MaximumParallelTests { get; set; }
     }
-    public sealed class ReportSettings
-    {
-        public bool ExpandClassTimeline { get; set; }
-    }
     public sealed class TUnitSettings
     {
         public . Display { get; }
         public . Execution { get; }
         public . Parallelism { get; }
-        public . Report { get; }
         public . Timeouts { get; }
     }
     public sealed class TimeoutSettings

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

@@ -381,6 +381,15 @@ namespace
         public static .ClassMetadata GetOrAdd(string name, <.ClassMetadata> factory) { }
         public static .ClassMetadata GetOrAdd(string name, .ClassMetadata value) { }
     }
+    [(.Assembly | .Class)]
+    public sealed class ClassTimelineAttribute : .TUnitAttribute, .IScopedAttribute, ., .
+    {
+        public ClassTimelineAttribute(. mode) { }
+        public . Mode { get; }
+        public int Order { get; }
+        public  ScopeType { get; }
+        public . OnTestDiscovered(.DiscoveredTestContext context) { }
+    }
     [(.Class | .Method)]
     public sealed class CombinedDataSourcesAttribute : .AsyncUntypedDataSourceGeneratorAttribute
     {
@@ -1934,6 +1943,11 @@ namespace .Enums
         Generated = 2,
         Derived = 3,
     }
+    public enum TimelineMode
+    {
+        Collapsed = 0,
+        FullExecution = 1,
+    }
 }
 namespace .Events
 {
@@ -2975,16 +2989,11 @@ namespace .Settings
     {
         public int? MaximumParallelTests { get; set; }
     }
-    public sealed class ReportSettings
-    {
-        public bool ExpandClassTimeline { get; set; }
-    }
     public sealed class TUnitSettings
     {
         public . Display { get; }
         public . Execution { get; }
         public . Parallelism { get; }
-        public . Report { get; }
         public . Timeouts { get; }
     }
     public sealed class TimeoutSettings