review fixes

src/NUnitFramework/framework/Api/NUnitTestAssemblyRunner.cs

@@ -344,6 +344,7 @@ private static int CountTestCases(ITest test, ITestFilter filter)
             if (!test.IsSuite)
                 return filter.Pass(test) ? 1: 0;
 
+            // Use for-loop to avoid allocating the enumerator
             int count = 0;
             var tests = test.Tests;
             for (var i = 0; i < tests.Count; i++)

src/NUnitFramework/framework/Internal/Filters/AndFilter.cs

@@ -30,6 +30,8 @@ internal sealed class AndFilter : CompositeFilter
         /// <returns>True if all the component filters pass, otherwise false</returns>
         public override bool Pass( ITest test, bool negated )
         {
+            // Use foreach-loop against array instead of LINQ for best performance
+
             if (negated)
             {
                 foreach (var filter in Filters)
@@ -61,6 +63,7 @@ public override bool Pass( ITest test, bool negated )
         /// <returns>True if all the component filters match, otherwise false</returns>
         public override bool Match( ITest test )
         {
+            // Use foreach-loop against array instead of LINQ for best performance
             foreach (var filter in Filters)
             {
                 if (!filter.Match(test))
@@ -79,6 +82,7 @@ public override bool Match( ITest test )
         /// <returns>True if all the component filters explicit match, otherwise false</returns>
         public override bool IsExplicitMatch( ITest test )
         {
+            // Use foreach-loop against array instead of LINQ for best performance
             foreach (var filter in Filters)
             {
                 if (!filter.IsExplicitMatch(test))

src/NUnitFramework/framework/Internal/Filters/CategoryFilter.cs

@@ -27,6 +27,7 @@ public override bool Match(ITest test)
         {
             if (test.Properties.TryGet(PropertyNames.Category, out var testCategories))
             {
+                // Use for-loop to avoid allocating the enumerator
                 for (var i = 0; i < testCategories.Count; ++i)
                 {
                     if (Match((string) testCategories[i]))

src/NUnitFramework/framework/Internal/Filters/InFilter.cs

@@ -43,7 +43,7 @@ public static bool TryOptimize(OrFilter orFilter, [NotNullWhen(true)] out InFilt
             // eagerly build expected value collection
             var expectedValues = new List<string?>(orFilter.Filters.Length);
 
-            // use for for faster traversal without boxed enumerator
+            // Use foreach-loop against array instead of LINQ for best performance
             foreach (var filter in orFilter.Filters)
             {
                 // make sure invariants are valid
@@ -79,7 +79,7 @@ public static bool TryOptimize(OrFilter orFilter, [NotNullWhen(true)] out InFilt
                     NamespaceFilter _ => test => test.TypeInfo?.Namespace,
                     TestNameFilter _ => test => test.Name,
                     _ => throw new InvalidOperationException("Invalid filter, logic wrong")
-                }; 
+                };
                 string xmlElementName = orFilter.Filters[0] switch
                 {
                     ClassNameFilter _ => ClassNameFilter.XmlElementName,

src/NUnitFramework/framework/Internal/Filters/OrFilter.cs

@@ -34,6 +34,8 @@ public OrFilter(params TestFilter[] filters) : base(filters)
         /// <returns>True if any of the component filters pass, otherwise false</returns>
         public override bool Pass( ITest test, bool negated )
         {
+            // Use foreach-loop against array instead of LINQ for best performance
+
             if (negated)
             {
                 foreach (var filter in Filters)
@@ -65,6 +67,7 @@ public override bool Pass( ITest test, bool negated )
         /// <returns>True if any of the component filters match, otherwise false</returns>
         public override bool Match( ITest test )
         {
+            // Use foreach-loop against array instead of LINQ for best performance
             foreach (var filter in Filters)
             {
                 if (filter.Match(test))
@@ -83,6 +86,7 @@ public override bool Match( ITest test )
         /// <returns>True if any of the component filters explicit match, otherwise false</returns>
         public override bool IsExplicitMatch( ITest test )
         {
+            // Use foreach-loop against array instead of LINQ for best performance
             foreach (var filter in Filters)
             {
                 if (filter.IsExplicitMatch(test))

src/NUnitFramework/framework/Internal/Filters/PropertyFilter.cs

@@ -32,6 +32,7 @@ public override bool Match(ITest test)
         {
             if (test.Properties.TryGet(_propertyName, out var values))
             {
+                // Use for-loop to avoid allocating the enumerator
                 for (var i = 0; i < values.Count; ++i)
                 {
                     if (Match((string) values[i]))

src/NUnitFramework/framework/Internal/PreFilter.cs

@@ -198,6 +198,7 @@ private bool MatchMethodElement(Type type)
 
             private bool MatchSetUpFixture(Type type)
             {
+                // checking length instead of for example LINQ .Any(), which would need to box array into IEnumerable
                 return IsSubNamespace(type.Namespace) &&
                        type.GetCustomAttributes(typeof(SetUpFixtureAttribute), true).Length > 0;
             }

src/NUnitFramework/framework/Internal/PropertyBag.cs

@@ -142,6 +142,7 @@ public TNode AddToXml(TNode parentNode, bool recursive)
         {
             TNode properties = parentNode.AddElement("properties");
 
+            // enumerating dictionary directly with struct enumerator which is fastest
             foreach (var pair in inner)
             {
                 foreach (var value in pair.Value)

src/NUnitFramework/framework/Internal/TestFilter.cs

@@ -111,11 +111,11 @@ protected virtual bool MatchDescendant(ITest test)
         /// </summary>
         public static TestFilter FromXml(string xmlText)
         {
-            const string emptyFilterXml1 = "<filter />";
-            const string emptyFilterXml2 = "<filter/>";
+            const string emptyFilterXmlWithSpace = "<filter />";
+            const string emptyFilterWithoutSpace = "<filter/>";
 
             // check for fast cases
-            if (string.IsNullOrEmpty(xmlText) || xmlText.Length < 11 && xmlText is emptyFilterXml1 or emptyFilterXml2)
+            if (string.IsNullOrEmpty(xmlText) || xmlText.Length < 11 && xmlText is emptyFilterXmlWithSpace or emptyFilterWithoutSpace)
             {
                 return Empty;
             }

src/NUnitFramework/framework/Internal/Tests/TestSuite.cs

@@ -222,9 +222,11 @@ public override int TestCaseCount
             {
                 int count = 0;
 
-                for (var i = 0; i < Tests.Count; i++)
+                // Use for-loop to avoid allocating the enumerator
+                var testsToCheck = Tests;
+                for (var i = 0; i < testsToCheck.Count; i++)
                 {
-                    count += Tests[i].TestCaseCount;
+                    count += testsToCheck[i].TestCaseCount;
                 }
 
                 return count;
@@ -293,8 +295,15 @@ public override TNode AddToXml(TNode parentNode, bool recursive)
 
 
             if (recursive)
-                foreach (Test test in this.Tests)
+            {
+                // Use for-loop to avoid allocating the enumerator
+                var testsToAdd = Tests;
+                for (var i = 0; i < testsToAdd.Count; i++)
+                {
+                    var test = testsToAdd[i];
                     test.AddToXml(thisNode, recursive);
+                }
+            }
 
             return thisNode;
         }