diff --git a/SysML2.NET.Tests/Extend/AcceptActionUsageExtensionsTestFixture.cs b/SysML2.NET.Tests/Extend/AcceptActionUsageExtensionsTestFixture.cs
index 58028a42..520487f5 100644
--- a/SysML2.NET.Tests/Extend/AcceptActionUsageExtensionsTestFixture.cs
+++ b/SysML2.NET.Tests/Extend/AcceptActionUsageExtensionsTestFixture.cs
@@ -1,50 +1,97 @@
 // -------------------------------------------------------------------------------------------------
 // <copyright file="AcceptActionUsageExtensionsTestFixture.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.Types;
     using SysML2.NET.Core.POCO.Systems.Actions;
+    using SysML2.NET.Core.POCO.Systems.States;
+    using SysML2.NET.Extensions;
 
     [TestFixture]
     public class AcceptActionUsageExtensionsTestFixture
     {
         [Test]
-        public void ComputePayloadArgument_ThrowsNotSupportedException()
+        public void VerifyComputePayloadArgument()
+        {
+            Assert.That(() => ((IAcceptActionUsage)null).ComputePayloadArgument(), Throws.TypeOf<ArgumentNullException>());
+
+            var accept = new AcceptActionUsage();
+
+            // For Later: populated case depends on ActionUsageExtensions.ComputeArgumentOperation at SysML2.NET/Extend/ActionUsageExtensions.cs:157, which is still a stub.
+            Assert.That(() => accept.ComputePayloadArgument(), Throws.TypeOf<NotSupportedException>());
+        }
+
+        [Test]
+        public void VerifyComputePayloadParameter()
         {
-            Assert.That(() => ((IAcceptActionUsage)null).ComputePayloadArgument(), Throws.TypeOf<NotSupportedException>());
+            Assert.That(() => ((IAcceptActionUsage)null).ComputePayloadParameter(), Throws.TypeOf<ArgumentNullException>());
+
+            var accept = new AcceptActionUsage();
+
+            // For Later: populated case depends on StepExtensions.ComputeParameter at SysML2.NET/Extend/StepExtensions.cs:71, which is still a stub.
+            Assert.That(() => accept.ComputePayloadParameter(), Throws.TypeOf<NotSupportedException>());
         }
-        
+
         [Test]
-        public void ComputePayloadParameter_ThrowsNotSupportedException()
+        public void VerifyComputeReceiverArgument()
         {
-            Assert.That(() => ((IAcceptActionUsage)null).ComputePayloadParameter(), Throws.TypeOf<NotSupportedException>());
+            Assert.That(() => ((IAcceptActionUsage)null).ComputeReceiverArgument(), Throws.TypeOf<ArgumentNullException>());
+
+            var accept = new AcceptActionUsage();
+
+            // For Later: populated case depends on ActionUsageExtensions.ComputeArgumentOperation at SysML2.NET/Extend/ActionUsageExtensions.cs:157, which is still a stub.
+            Assert.That(() => accept.ComputeReceiverArgument(), Throws.TypeOf<NotSupportedException>());
         }
-        
+
         [Test]
-        public void ComputeReceiverArgument_ThrowsNotSupportedException()
+        public void VerifyComputeIsTriggerActionOperation()
         {
-            Assert.That(() => ((IAcceptActionUsage)null).ComputeReceiverArgument(), Throws.TypeOf<NotSupportedException>());
+            Assert.That(() => ((IAcceptActionUsage)null).ComputeIsTriggerActionOperation(), Throws.TypeOf<ArgumentNullException>());
+
+            // Branch A — null owningType: no OwningRelationship set, so owningType is null → false.
+            var acceptNoOwner = new AcceptActionUsage();
+
+            Assert.That(acceptNoOwner.ComputeIsTriggerActionOperation(), Is.False);
+
+            // Branch B — non-null owningType, not ITransitionUsage: owner is ActionDefinition → false.
+            var actionDefinitionOwner = new ActionDefinition();
+            var featureMembershipB = new FeatureMembership();
+            actionDefinitionOwner.AssignOwnership(featureMembershipB, new AcceptActionUsage());
+            var acceptNotTransition = new AcceptActionUsage();
+            actionDefinitionOwner.AssignOwnership(new FeatureMembership(), acceptNotTransition);
+
+            Assert.That(acceptNotTransition.ComputeIsTriggerActionOperation(), Is.False);
+
+            // Branch C — owningType IS ITransitionUsage: triggerAction dispatch hits the ComputeTriggerAction stub.
+            var transitionOwner = new TransitionUsage();
+            var featureMembershipC = new FeatureMembership();
+            var acceptInTransition = new AcceptActionUsage();
+            transitionOwner.AssignOwnership(featureMembershipC, acceptInTransition);
+
+            // For Later: populated case depends on TransitionUsageExtensions.ComputeTriggerAction at SysML2.NET/Extend/TransitionUsageExtensions.cs:208, which is still a stub.
+            Assert.That(() => acceptInTransition.ComputeIsTriggerActionOperation(), Throws.TypeOf<NotSupportedException>());
         }
     }
 }
diff --git a/SysML2.NET/Extend/AcceptActionUsageExtensions.cs b/SysML2.NET/Extend/AcceptActionUsageExtensions.cs
index d569c554..b970aaa8 100644
--- a/SysML2.NET/Extend/AcceptActionUsageExtensions.cs
+++ b/SysML2.NET/Extend/AcceptActionUsageExtensions.cs
@@ -78,10 +78,11 @@ internal static class AcceptActionUsageExtensions
         /// <returns>
         /// the computed result
         /// </returns>
-        [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
         internal static IExpression ComputePayloadArgument(this IAcceptActionUsage acceptActionUsageSubject)
         {
-            throw new NotSupportedException("Create a GitHub issue when this method is required");
+            return acceptActionUsageSubject == null
+                ? throw new ArgumentNullException(nameof(acceptActionUsageSubject))
+                : acceptActionUsageSubject.Argument(1);
         }
 
         /// <summary>
@@ -101,10 +102,18 @@ internal static IExpression ComputePayloadArgument(this IAcceptActionUsage accep
         /// <returns>
         /// the computed result
         /// </returns>
-        [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
         internal static IReferenceUsage ComputePayloadParameter(this IAcceptActionUsage acceptActionUsageSubject)
         {
-            throw new NotSupportedException("Create a GitHub issue when this method is required");
+            if (acceptActionUsageSubject == null)
+            {
+                throw new ArgumentNullException(nameof(acceptActionUsageSubject));
+            }
+
+            var parameters = acceptActionUsageSubject.parameter;
+
+            return parameters.Count == 0
+                ? null
+                : parameters[0] as IReferenceUsage;
         }
 
         /// <summary>
@@ -122,10 +131,11 @@ internal static IReferenceUsage ComputePayloadParameter(this IAcceptActionUsage
         /// <returns>
         /// the computed result
         /// </returns>
-        [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
         internal static IExpression ComputeReceiverArgument(this IAcceptActionUsage acceptActionUsageSubject)
         {
-            throw new NotSupportedException("Create a GitHub issue when this method is required");
+            return acceptActionUsageSubject == null
+                ? throw new ArgumentNullException(nameof(acceptActionUsageSubject))
+                : acceptActionUsageSubject.Argument(2);
         }
 
         /// <summary>
@@ -145,10 +155,12 @@ internal static IExpression ComputeReceiverArgument(this IAcceptActionUsage acce
         /// <returns>
         /// The expected <see cref="bool" />
         /// </returns>
-        [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
         internal static bool ComputeIsTriggerActionOperation(this IAcceptActionUsage acceptActionUsageSubject)
         {
-            throw new NotSupportedException("Create a GitHub issue when this method is required");
+            return acceptActionUsageSubject == null
+                ? throw new ArgumentNullException(nameof(acceptActionUsageSubject))
+                : acceptActionUsageSubject.owningType is ITransitionUsage transitionUsage
+                  && transitionUsage.triggerAction.Contains(acceptActionUsageSubject);
         }
     }
 }