perf: cache attribute factory results on TestMetadata

Add GetOrCreateAttributes() that lazily caches the attribute array on
first call. AttributeFactory was being invoked multiple times per test
during building — now it runs once and subsequent calls return the cached
array, avoiding redundant attribute instantiation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: thomhurst

TUnit.Core/GenericTestMetadata.cs

@@ -66,7 +66,7 @@ public override Func<ExecutableTestCreationContext, TestMetadata, AbstractExecut
                 Func<TestContext, Task<object>> createInstance = async (testContext) =>
                 {
                     // Try to create instance with ClassConstructor attribute
-                    var attributes = metadata.AttributeFactory();
+                    var attributes = metadata.GetOrCreateAttributes();
                     var classInstance = await ClassConstructorHelper.TryCreateInstanceWithClassConstructor(
                         attributes,
                         TestClassType,

TUnit.Core/TestMetadata.cs

@@ -49,6 +49,17 @@ public abstract class TestMetadata
 
     public required Func<Attribute[]> AttributeFactory { get; init; }
 
+    private Attribute[]? _cachedAttributes;
+
+    /// <summary>
+    /// Returns the cached attributes array, creating it from <see cref="AttributeFactory"/> on first call.
+    /// Subsequent calls return the same array without re-invoking the factory.
+    /// </summary>
+    internal Attribute[] GetOrCreateAttributes()
+    {
+        return _cachedAttributes ??= AttributeFactory();
+    }
+
     /// <summary>
     /// Pre-extracted repeat count from RepeatAttribute.
     /// Null if no repeat attribute is present (defaults to 0 at usage site).

TUnit.Core/TestMetadata`1.cs

@@ -86,7 +86,7 @@ public override Func<ExecutableTestCreationContext, TestMetadata, AbstractExecut
                             return await context.TestClassInstanceFactory();
                         }
 
-                        var attributes = metadata.AttributeFactory();
+                        var attributes = metadata.GetOrCreateAttributes();
                         var instance = await ClassConstructorHelper.TryCreateInstanceWithClassConstructor(
                             attributes,
                             TestClassType,

TUnit.Engine/Building/TestBuilder.cs

@@ -73,7 +73,7 @@ private async Task<object> CreateInstance(TestMetadata metadata, Type[] resolved
 
         // First try to create instance with ClassConstructor attribute
         // Use attributes from context if available
-        var attributes = builderContext.InitializedAttributes ?? metadata.AttributeFactory();
+        var attributes = builderContext.InitializedAttributes ?? metadata.GetOrCreateAttributes();
 
         var instance = await ClassConstructorHelper.TryCreateInstanceWithClassConstructor(
             attributes,
@@ -154,7 +154,7 @@ public async Task<IEnumerable<AbstractExecutableTest>> BuildTestsFromMetadataAsy
             var repeatCount = metadata.RepeatCount ?? 0;
 
             // Create and initialize attributes ONCE
-            var attributes = await InitializeAttributesAsync(metadata.AttributeFactory.Invoke());
+            var attributes = await InitializeAttributesAsync(metadata.GetOrCreateAttributes());
 
             if (metadata.ClassDataSources.Any(ds => ds is IAccessesInstanceData))
             {
@@ -1017,7 +1017,7 @@ private static void CollectAllDependencies(AbstractExecutableTest test, HashSet<
     /// </summary>
     private static string? GetBasicSkipReason(TestMetadata metadata, Attribute[]? cachedAttributes = null)
     {
-        var attributes = cachedAttributes ?? metadata.AttributeFactory();
+        var attributes = cachedAttributes ?? metadata.GetOrCreateAttributes();
 
         SkipAttribute? firstSkipAttribute = null;
 
@@ -1047,7 +1047,7 @@ private static void CollectAllDependencies(AbstractExecutableTest test, HashSet<
     private async ValueTask<TestContext> CreateTestContextAsync(string testId, TestMetadata metadata, TestData testData, TestBuilderContext testBuilderContext)
     {
         // Use attributes from context if available, or create new ones
-        var attributes = testBuilderContext.InitializedAttributes ?? await InitializeAttributesAsync(metadata.AttributeFactory.Invoke());
+        var attributes = testBuilderContext.InitializedAttributes ?? await InitializeAttributesAsync(metadata.GetOrCreateAttributes());
 
         if (testBuilderContext.DataSourceAttribute != null && testBuilderContext.DataSourceAttribute is not NoDataSource)
         {
@@ -1138,7 +1138,7 @@ private async Task<AbstractExecutableTest> CreateFailedTestForDataGenerationErro
 
     private async Task<TestDetails> CreateFailedTestDetails(TestMetadata metadata, string testId)
     {
-        var attributes = (await InitializeAttributesAsync(metadata.AttributeFactory.Invoke()));
+        var attributes = (await InitializeAttributesAsync(metadata.GetOrCreateAttributes()));
         return new TestDetails(attributes)
         {
             TestId = testId,
@@ -1524,7 +1524,7 @@ public async IAsyncEnumerable<AbstractExecutableTest> BuildTestsStreamingAsync(
         var repeatCount = metadata.RepeatCount ?? 0;
 
         // Initialize attributes
-        var attributes = await InitializeAttributesAsync(metadata.AttributeFactory.Invoke());
+        var attributes = await InitializeAttributesAsync(metadata.GetOrCreateAttributes());
 
         // Create base context with ClassConstructor if present
         // StateBag and Events are lazy-initialized for performance

TUnit.Engine/Building/TestBuilderPipeline.cs

@@ -54,7 +54,7 @@ private TestBuilderContext CreateTestBuilderContext(TestMetadata metadata)
         };
 
         // Check for ClassConstructor attribute and set it early if present
-        var attributes = metadata.AttributeFactory();
+        var attributes = metadata.GetOrCreateAttributes();
 
         // Look for any attribute that inherits from ClassConstructorAttribute
         // This handles both ClassConstructorAttribute and ClassConstructorAttribute<T>
@@ -246,7 +246,7 @@ private async Task<AbstractExecutableTest[]> GenerateDynamicTests(TestMetadata m
                 : baseDisplayName;
 
             // Get attributes first
-            var attributes = metadata.AttributeFactory();
+            var attributes = metadata.GetOrCreateAttributes();
 
             // Create TestDetails for dynamic tests
             var testDetails = new TestDetails(attributes)
@@ -345,7 +345,7 @@ private async IAsyncEnumerable<AbstractExecutableTest> BuildTestsFromSingleMetad
                 var repeatCount = resolvedMetadata.RepeatCount ?? 0;
 
                 // Get attributes for test details
-                var attributes = resolvedMetadata.AttributeFactory?.Invoke() ?? [];
+                var attributes = resolvedMetadata.GetOrCreateAttributes();
 
                 // Dynamic tests need to honor attributes like RepeatCount, RetryCount, etc.
                 // We'll create multiple test instances based on RepeatCount