fix(html-report): extract categories using MTP Key=name convention

TUnit.Engine.Tests/HtmlReporterTests.cs

@@ -262,6 +262,43 @@ public void GenerateHtml_RoundTrips_ClassTimeline_CustomProperty_OnTest()
         embedded.ShouldContain("\"value\":\"FullExecution\"");
     }
 
+    [Test]
+    public void ExtractTestResult_SortsTestMetadataProperty_Into_Categories_And_CustomProperties()
+    {
+        // Regression: Microsoft.Testing.Platform's VSTestBridge convention emits categories as
+        // TestMetadataProperty(name, "") — the category name lives in Key, Value is empty.
+        // Traits/custom properties use the (key, value) form with a non-empty Value.
+        // Earlier code keyed off IsNullOrEmpty(Key), which inverted both branches and silently
+        // misclassified every category as a custom property — leaving the HTML report's
+        // category-pill UI permanently empty.
+        var node = new TestNode
+        {
+            Uid = new TestNodeUid("extract-1"),
+            DisplayName = "Test",
+            Properties = new PropertyBag(
+                PassedTestNodeStateProperty.CachedInstance,
+                new TestMethodIdentifierProperty(
+                    @namespace: "TestNamespace",
+                    assemblyFullName: "TestAssembly",
+                    typeName: "SampleTests",
+                    methodName: "Test",
+                    parameterTypeFullNames: [],
+                    returnTypeFullName: "System.Void",
+                    methodArity: 0),
+                new TestMetadataProperty("Async", string.Empty),
+                new TestMetadataProperty("Integration", string.Empty),
+                new TestMetadataProperty("Owner", "TeamA"))
+        };
+
+        var result = HtmlReporter.ExtractTestResult("extract-1", node, traceId: null, spanId: null, retryAttempt: 0, additionalTraceIds: null);
+
+        result.Categories.ShouldBe(["Async", "Integration"], ignoreOrder: true);
+        result.CustomProperties.ShouldNotBeNull();
+        result.CustomProperties!.Length.ShouldBe(1);
+        result.CustomProperties[0].Key.ShouldBe("Owner");
+        result.CustomProperties[0].Value.ShouldBe("TeamA");
+    }
+
     private static ReportTestResult CreateTestResultWithStartTime(string displayName, string? startTime) => new()
     {
         Id = displayName,

TUnit.Engine/Reporters/Html/HtmlReporter.cs

@@ -484,7 +484,7 @@ private static DateTimeOffset ParseStartTimeForSort(string? raw)
             : DateTimeOffset.MaxValue;
     }
 
-    private static ReportTestResult ExtractTestResult(string testId, TestNode testNode, string? traceId, string? spanId, int retryAttempt, string[]? additionalTraceIds)
+    internal static ReportTestResult ExtractTestResult(string testId, TestNode testNode, string? traceId, string? spanId, int retryAttempt, string[]? additionalTraceIds)
     {
         IProperty? stateProperty = null;
         TestMethodIdentifierProperty? testMethodIdentifier = null;
@@ -518,10 +518,13 @@ private static ReportTestResult ExtractTestResult(string testId, TestNode testNo
                     stdErr = TruncateOutput(e.StandardError);
                     break;
                 case TestMetadataProperty meta:
-                    if (string.IsNullOrEmpty(meta.Key))
+                    // MTP convention (matches Microsoft.Testing.Extensions.VSTestBridge): categories are
+                    // emitted as TestMetadataProperty(category, "") — name in Key, empty Value. Traits/
+                    // custom properties use (key, value) with a non-empty Value.
+                    if (string.IsNullOrEmpty(meta.Value))
                     {
                         categories ??= [];
-                        categories.Add(meta.Value);
+                        categories.Add(meta.Key);
                     }
                     else
                     {