perf: eliminate OfType iterator allocation with manual looping (#4513)

Author: TimothyMakkison

TUnit.Core/Helpers/ClassConstructorHelper.cs

@@ -43,7 +43,7 @@ public static class ClassConstructorHelper
         TestBuilderContext testBuilderContext,
         string testSessionId)
     {
-        var classConstructorAttribute = attributes.OfType<ClassConstructorAttribute>().FirstOrDefault();
+        var classConstructorAttribute = GetClassConstructorAttribute(attributes);
 
         if (classConstructorAttribute == null)
         {
@@ -78,6 +78,21 @@ public static bool HasClassConstructorAttribute(Attribute[] attributes)
     /// </summary>
     public static ClassConstructorAttribute? GetClassConstructorAttribute(Attribute[] attributes)
     {
-        return attributes.OfType<ClassConstructorAttribute>().FirstOrDefault();
+        return GetClassConstructorAttribute((IReadOnlyList<ClassConstructorAttribute>)attributes);
+    }
+
+    private static ClassConstructorAttribute? GetClassConstructorAttribute(IReadOnlyList<Attribute> attributes)
+    {
+        ClassConstructorAttribute? classConstructorAttribute = null;
+        foreach (Attribute attribute in attributes)
+        {
+            if (attribute is ClassConstructorAttribute classAttribute)
+            {
+                classConstructorAttribute = classAttribute;
+                break;
+            }
+        }
+
+        return classConstructorAttribute;
     }
 }

TUnit.Engine/Building/TestBuilder.cs

@@ -949,13 +949,17 @@ public async Task<AbstractExecutableTest> BuildTestAsync(TestMetadata metadata,
     private static string? GetBasicSkipReason(TestMetadata metadata, Attribute[]? cachedAttributes = null)
     {
         var attributes = cachedAttributes ?? metadata.AttributeFactory();
-        var skipAttributes = attributes.OfType<SkipAttribute>();
 
         SkipAttribute? firstSkipAttribute = null;
 
         // Check if all skip attributes are basic (non-derived) SkipAttribute instances
-        foreach (var skipAttribute in skipAttributes)
+        foreach (var attribute in attributes)
         {
+            if (attribute is not SkipAttribute skipAttribute)
+            {
+                continue;
+            }
+
             firstSkipAttribute ??= skipAttribute;
 
             var attributeType = skipAttribute.GetType();