diff --git a/SysML2.NET.Tests/Extend/ConjugatedPortTypingExtensionsTestFixture.cs b/SysML2.NET.Tests/Extend/ConjugatedPortTypingExtensionsTestFixture.cs
index 34b4840b..1fa1434c 100644
--- a/SysML2.NET.Tests/Extend/ConjugatedPortTypingExtensionsTestFixture.cs
+++ b/SysML2.NET.Tests/Extend/ConjugatedPortTypingExtensionsTestFixture.cs
@@ -1,38 +1,56 @@
-// -------------------------------------------------------------------------------------------------
+// -------------------------------------------------------------------------------------------------
 // <copyright file="ConjugatedPortTypingExtensionsTestFixture.cs" company="Starion Group S.A.">
-// 
+//
 //   Copyright 2022-2026 Starion Group S.A.
-// 
+//
 //   Licensed under the Apache License, Version 2.0 (the "License");
 //   you may not use this file except in compliance with the License.
 //   You may obtain a copy of the License at
-// 
+//
 //        http://www.apache.org/licenses/LICENSE-2.0
-// 
+//
 //    Unless required by applicable law or agreed to in writing, software
 //    distributed under the License is distributed on an "AS IS" BASIS,
 //    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 //    See the License for the specific language governing permissions and
 //    limitations under the License.
-// 
+//
 // </copyright>
 // ------------------------------------------------------------------------------------------------
 
 namespace SysML2.NET.Tests.Extend
 {
     using System;
-    
+
     using NUnit.Framework;
-    
+
+    using SysML2.NET.Core.POCO.Root.Namespaces;
     using SysML2.NET.Core.POCO.Systems.Ports;
+    using SysML2.NET.Extensions;
 
     [TestFixture]
     public class ConjugatedPortTypingExtensionsTestFixture
     {
         [Test]
-        public void ComputePortDefinition_ThrowsNotSupportedException()
+        public void VerifyComputePortDefinition()
         {
-            Assert.That(() => ((IConjugatedPortTyping)null).ComputePortDefinition(), Throws.TypeOf<NotSupportedException>());
+            Assert.That(() => ((IConjugatedPortTyping)null).ComputePortDefinition(), Throws.TypeOf<ArgumentNullException>());
+
+            // No ConjugatedPortDefinition -> the null-safe navigation short-circuits to null.
+            var emptyConjugatedPortTyping = new ConjugatedPortTyping();
+
+            Assert.That(emptyConjugatedPortTyping.ComputePortDefinition(), Is.Null);
+
+            // Positive case: the ConjugatedPortDefinition's originalPortDefinition derives from its
+            // owningMembership -> membershipOwningNamespace, which must be a PortDefinition. Wire that
+            // ownership chain so originalPortDefinition (and thus portDefinition) resolves to the original.
+            var originalPortDefinition = new PortDefinition();
+            var conjugatedPortDefinition = new ConjugatedPortDefinition();
+            originalPortDefinition.AssignOwnership(new OwningMembership(), conjugatedPortDefinition);
+
+            var conjugatedPortTyping = new ConjugatedPortTyping { ConjugatedPortDefinition = conjugatedPortDefinition };
+
+            Assert.That(conjugatedPortTyping.ComputePortDefinition(), Is.SameAs(originalPortDefinition));
         }
     }
 }
diff --git a/SysML2.NET.Tests/Extend/ControlNodeExtensionsTestFixture.cs b/SysML2.NET.Tests/Extend/ControlNodeExtensionsTestFixture.cs
new file mode 100644
index 00000000..b4cf7acc
--- /dev/null
+++ b/SysML2.NET.Tests/Extend/ControlNodeExtensionsTestFixture.cs
@@ -0,0 +1,82 @@
+// -------------------------------------------------------------------------------------------------
+// <copyright file="ControlNodeExtensionsTestFixture.cs" company="Starion Group S.A.">
+//
+//   Copyright 2022-2026 Starion Group S.A.
+//
+//   Licensed under the Apache License, Version 2.0 (the "License");
+//   you may not use this file except in compliance with the License.
+//   You may obtain a copy of the License at
+//
+//        http://www.apache.org/licenses/LICENSE-2.0
+//
+//    Unless required by applicable law or agreed to in writing, software
+//    distributed under the License is distributed on an "AS IS" BASIS,
+//    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//    See the License for the specific language governing permissions and
+//    limitations under the License.
+//
+// </copyright>
+// ------------------------------------------------------------------------------------------------
+
+namespace SysML2.NET.Tests.Extend
+{
+    using System;
+
+    using Moq;
+
+    using NUnit.Framework;
+
+    using SysML2.NET.Core.POCO.Core.Types;
+    using SysML2.NET.Core.POCO.Kernel.Multiplicities;
+    using SysML2.NET.Core.POCO.Systems.Actions;
+
+    [TestFixture]
+    public class ControlNodeExtensionsTestFixture
+    {
+        [Test]
+        public void VerifyComputeMultiplicityHasBoundsOperation()
+        {
+            // ControlNode is abstract; ForkNode is a concrete IControlNode used as the subject.
+            var controlNode = new ForkNode();
+
+            Assert.That(() => ((IControlNode)null).ComputeMultiplicityHasBoundsOperation(null, 1, "1"), Throws.TypeOf<ArgumentNullException>());
+
+            // mult == null -> false (the OCL "mult <> null" guard, not a throw).
+            Assert.That(controlNode.ComputeMultiplicityHasBoundsOperation(null, 1, "1"), Is.False);
+
+            // mult IS a MultiplicityRange -> the direct branch delegates to HasBounds(lower, upper).
+            var range = new Mock<IMultiplicityRange>();
+            range.Setup(x => x.HasBounds(1, "5")).Returns(true);
+
+            using (Assert.EnterMultipleScope())
+            {
+                Assert.That(controlNode.ComputeMultiplicityHasBoundsOperation(range.Object, 1, "5"), Is.True);
+
+                // Bounds that were not set up return Moq's default (false).
+                Assert.That(controlNode.ComputeMultiplicityHasBoundsOperation(range.Object, 0, "5"), Is.False);
+            }
+
+            // mult is a plain Multiplicity (NOT a MultiplicityRange) -> the supertype branch searches
+            // AllSupertypes() for a MultiplicityRange whose HasBounds(lower, upper) is true.
+            var rangeSupertype = new Mock<IMultiplicityRange>();
+            rangeSupertype.Setup(x => x.HasBounds(1, "5")).Returns(true);
+
+            var multiplicityWithRangeSupertype = new Mock<IMultiplicity>();
+            multiplicityWithRangeSupertype.Setup(x => x.AllSupertypes()).Returns([rangeSupertype.Object]);
+
+            var multiplicityWithoutRangeSupertype = new Mock<IMultiplicity>();
+            multiplicityWithoutRangeSupertype.Setup(x => x.AllSupertypes()).Returns([]);
+
+            using (Assert.EnterMultipleScope())
+            {
+                Assert.That(controlNode.ComputeMultiplicityHasBoundsOperation(multiplicityWithRangeSupertype.Object, 1, "5"), Is.True);
+
+                // A matching MultiplicityRange supertype exists, but the requested bounds do not match.
+                Assert.That(controlNode.ComputeMultiplicityHasBoundsOperation(multiplicityWithRangeSupertype.Object, 0, "5"), Is.False);
+
+                // No MultiplicityRange among the supertypes -> false.
+                Assert.That(controlNode.ComputeMultiplicityHasBoundsOperation(multiplicityWithoutRangeSupertype.Object, 1, "5"), Is.False);
+            }
+        }
+    }
+}
diff --git a/SysML2.NET.Tests/Extend/FeatureTypingExtensionsTestFixture.cs b/SysML2.NET.Tests/Extend/FeatureTypingExtensionsTestFixture.cs
index 553e9ddb..b9f65d4c 100644
--- a/SysML2.NET.Tests/Extend/FeatureTypingExtensionsTestFixture.cs
+++ b/SysML2.NET.Tests/Extend/FeatureTypingExtensionsTestFixture.cs
@@ -1,38 +1,57 @@
-// -------------------------------------------------------------------------------------------------
+// -------------------------------------------------------------------------------------------------
 // <copyright file="FeatureTypingExtensionsTestFixture.cs" company="Starion Group S.A.">
-// 
+//
 //   Copyright 2022-2026 Starion Group S.A.
-// 
+//
 //   Licensed under the Apache License, Version 2.0 (the "License");
 //   you may not use this file except in compliance with the License.
 //   You may obtain a copy of the License at
-// 
+//
 //        http://www.apache.org/licenses/LICENSE-2.0
-// 
+//
 //    Unless required by applicable law or agreed to in writing, software
 //    distributed under the License is distributed on an "AS IS" BASIS,
 //    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 //    See the License for the specific language governing permissions and
 //    limitations under the License.
-// 
+//
 // </copyright>
 // ------------------------------------------------------------------------------------------------
 
 namespace SysML2.NET.Tests.Extend
 {
     using System;
-    
+
     using NUnit.Framework;
-    
+
     using SysML2.NET.Core.POCO.Core.Features;
+    using SysML2.NET.Core.POCO.Root.Elements;
+    using SysML2.NET.Core.POCO.Root.Namespaces;
 
     [TestFixture]
     public class FeatureTypingExtensionsTestFixture
     {
         [Test]
-        public void ComputeOwningFeature_ThrowsNotSupportedException()
+        public void VerifyComputeOwningFeature()
         {
-            Assert.That(() => ((IFeatureTyping)null).ComputeOwningFeature(), Throws.TypeOf<NotSupportedException>());
+            Assert.That(() => ((IFeatureTyping)null).ComputeOwningFeature(), Throws.TypeOf<ArgumentNullException>());
+
+            var featureTyping = new FeatureTyping();
+
+            Assert.That(featureTyping.ComputeOwningFeature(), Is.Null);
+
+            var feature = new Feature();
+
+            ((IContainedRelationship)featureTyping).OwningRelatedElement = feature;
+
+            Assert.That(featureTyping.ComputeOwningFeature(), Is.SameAs(feature));
+
+            var namespaceOwner = new Namespace();
+            var nonFeatureFeatureTyping = new FeatureTyping();
+
+            ((IContainedRelationship)nonFeatureFeatureTyping).OwningRelatedElement = namespaceOwner;
+
+            Assert.That(nonFeatureFeatureTyping.ComputeOwningFeature(), Is.Null);
         }
     }
 }
diff --git a/SysML2.NET.Tests/Extend/ReturnParameterMembershipExtensionsTestFixture.cs b/SysML2.NET.Tests/Extend/ReturnParameterMembershipExtensionsTestFixture.cs
new file mode 100644
index 00000000..142328ab
--- /dev/null
+++ b/SysML2.NET.Tests/Extend/ReturnParameterMembershipExtensionsTestFixture.cs
@@ -0,0 +1,43 @@
+// -------------------------------------------------------------------------------------------------
+// <copyright file="ReturnParameterMembershipExtensionsTestFixture.cs" company="Starion Group S.A.">
+//
+//   Copyright 2022-2026 Starion Group S.A.
+//
+//   Licensed under the Apache License, Version 2.0 (the "License");
+//   you may not use this file except in compliance with the License.
+//   You may obtain a copy of the License at
+//
+//        http://www.apache.org/licenses/LICENSE-2.0
+//
+//    Unless required by applicable law or agreed to in writing, software
+//    distributed under the License is distributed on an "AS IS" BASIS,
+//    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//    See the License for the specific language governing permissions and
+//    limitations under the License.
+//
+// </copyright>
+// ------------------------------------------------------------------------------------------------
+
+namespace SysML2.NET.Tests.Extend
+{
+    using System;
+
+    using NUnit.Framework;
+
+    using SysML2.NET.Core.Core.Types;
+    using SysML2.NET.Core.POCO.Kernel.Functions;
+
+    [TestFixture]
+    public class ReturnParameterMembershipExtensionsTestFixture
+    {
+        [Test]
+        public void VerifyComputeRedefinedParameterDirectionOperation()
+        {
+            Assert.That(() => ((IReturnParameterMembership)null).ComputeRedefinedParameterDirectionOperation(), Throws.TypeOf<ArgumentNullException>());
+
+            var returnParameterMembership = new ReturnParameterMembership();
+
+            Assert.That(returnParameterMembership.ComputeRedefinedParameterDirectionOperation(), Is.EqualTo(FeatureDirectionKind.Out));
+        }
+    }
+}
diff --git a/SysML2.NET/Extend/ConjugatedPortTypingExtensions.cs b/SysML2.NET/Extend/ConjugatedPortTypingExtensions.cs
index 807119a3..af5aff1b 100644
--- a/SysML2.NET/Extend/ConjugatedPortTypingExtensions.cs
+++ b/SysML2.NET/Extend/ConjugatedPortTypingExtensions.cs
@@ -50,10 +50,11 @@ internal static class ConjugatedPortTypingExtensions
         /// <returns>
         /// the computed result
         /// </returns>
-        [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
         internal static IPortDefinition ComputePortDefinition(this IConjugatedPortTyping conjugatedPortTypingSubject)
         {
-            throw new NotSupportedException("Create a GitHub issue when this method is required");
+            return conjugatedPortTypingSubject == null
+                ? throw new ArgumentNullException(nameof(conjugatedPortTypingSubject))
+                : conjugatedPortTypingSubject.ConjugatedPortDefinition?.originalPortDefinition;
         }
 
     }
diff --git a/SysML2.NET/Extend/ControlNodeExtensions.cs b/SysML2.NET/Extend/ControlNodeExtensions.cs
index 910f14f3..82604e14 100644
--- a/SysML2.NET/Extend/ControlNodeExtensions.cs
+++ b/SysML2.NET/Extend/ControlNodeExtensions.cs
@@ -22,10 +22,12 @@ namespace SysML2.NET.Core.POCO.Systems.Actions
 {
     using System;
     using System.Collections.Generic;
+    using System.Linq;
 
     using SysML2.NET.Core.Core.Types;
     using SysML2.NET.Core.Root.Namespaces;
     using SysML2.NET.Core.Systems.Occurrences;
+    using SysML2.NET.Core.POCO.Kernel.Multiplicities;
     using SysML2.NET.Core.POCO.Core.Classifiers;
     using SysML2.NET.Core.POCO.Core.Features;
     using SysML2.NET.Core.POCO.Core.Types;
@@ -95,10 +97,17 @@ internal static class ControlNodeExtensions
         /// <returns>
         /// The expected <see cref="bool" />
         /// </returns>
-        [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
         internal static bool ComputeMultiplicityHasBoundsOperation(this IControlNode controlNodeSubject, IMultiplicity mult, int lower, string upper)
         {
-            throw new NotSupportedException("Create a GitHub issue when this method is required");
+            if (controlNodeSubject == null)
+            {
+                throw new ArgumentNullException(nameof(controlNodeSubject));
+            }
+
+            return mult != null
+                && (mult is IMultiplicityRange multiplicityRange
+                    ? multiplicityRange.HasBounds(lower, upper)
+                    : mult.AllSupertypes().OfType<IMultiplicityRange>().Any(rangeSupertype => rangeSupertype.HasBounds(lower, upper)));
         }
     }
 }
diff --git a/SysML2.NET/Extend/FeatureTypingExtensions.cs b/SysML2.NET/Extend/FeatureTypingExtensions.cs
index 0b0762c1..47af06c1 100644
--- a/SysML2.NET/Extend/FeatureTypingExtensions.cs
+++ b/SysML2.NET/Extend/FeatureTypingExtensions.cs
@@ -43,10 +43,11 @@ internal static class FeatureTypingExtensions
         /// <returns>
         /// the computed result
         /// </returns>
-        [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
         internal static IFeature ComputeOwningFeature(this IFeatureTyping featureTypingSubject)
         {
-            throw new NotSupportedException("Create a GitHub issue when this method is required");
+            return featureTypingSubject == null
+                ? throw new ArgumentNullException(nameof(featureTypingSubject))
+                : featureTypingSubject.OwningRelatedElement as IFeature;
         }
 
     }
diff --git a/SysML2.NET/Extend/ReturnParameterMembershipExtensions.cs b/SysML2.NET/Extend/ReturnParameterMembershipExtensions.cs
index 44d92a18..3f283a64 100644
--- a/SysML2.NET/Extend/ReturnParameterMembershipExtensions.cs
+++ b/SysML2.NET/Extend/ReturnParameterMembershipExtensions.cs
@@ -54,10 +54,11 @@ internal static class ReturnParameterMembershipExtensions
         /// <returns>
         /// The expected <see cref="FeatureDirectionKind" />
         /// </returns>
-        [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
         internal static FeatureDirectionKind ComputeRedefinedParameterDirectionOperation(this IReturnParameterMembership returnParameterMembershipSubject)
         {
-            throw new NotSupportedException("Create a GitHub issue when this method is required");
+            return returnParameterMembershipSubject == null
+                ? throw new ArgumentNullException(nameof(returnParameterMembershipSubject))
+                : FeatureDirectionKind.Out;
         }
     }
 }