Index: Ringtoets/Integration/src/Ringtoets.Integration.Plugin/Merge/AssessmentSectionMergeHandler.cs
===================================================================
diff -u -rac2ef64a966ba1988c30df9773b383716e133eef -r0a3fd57580aff0d6487e195c67f315f628b1ced4
--- Ringtoets/Integration/src/Ringtoets.Integration.Plugin/Merge/AssessmentSectionMergeHandler.cs	(.../AssessmentSectionMergeHandler.cs)	(revision ac2ef64a966ba1988c30df9773b383716e133eef)
+++ Ringtoets/Integration/src/Ringtoets.Integration.Plugin/Merge/AssessmentSectionMergeHandler.cs	(.../AssessmentSectionMergeHandler.cs)	(revision 0a3fd57580aff0d6487e195c67f315f628b1ced4)
@@ -54,6 +54,27 @@
         public void PerformMerge(AssessmentSection targetAssessmentSection, AssessmentSection sourceAssessmentSection,
                                  IEnumerable<IFailureMechanism> failureMechanismsToMerge)
         {
+            if (targetAssessmentSection == null)
+            {
+                throw new ArgumentNullException(nameof(targetAssessmentSection));
+            }
+
+            if (sourceAssessmentSection == null)
+            {
+                throw new ArgumentNullException(nameof(sourceAssessmentSection));
+            }
+
+            if (failureMechanismsToMerge == null)
+            {
+                throw new ArgumentNullException(nameof(failureMechanismsToMerge));
+            }
+
+            BeforeMerge(targetAssessmentSection);
         }
+
+        private void BeforeMerge(AssessmentSection assessmentSection)
+        {
+            viewCommands.RemoveAllViewsForItem(assessmentSection);
+        }
     }
 }
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Index: Ringtoets/Integration/test/Ringtoets.Integration.Plugin.Test/Merge/AssessmentSectionMergeHandlerTest.cs
===================================================================
diff -u -rac2ef64a966ba1988c30df9773b383716e133eef -r0a3fd57580aff0d6487e195c67f315f628b1ced4
--- Ringtoets/Integration/test/Ringtoets.Integration.Plugin.Test/Merge/AssessmentSectionMergeHandlerTest.cs	(.../AssessmentSectionMergeHandlerTest.cs)	(revision ac2ef64a966ba1988c30df9773b383716e133eef)
+++ Ringtoets/Integration/test/Ringtoets.Integration.Plugin.Test/Merge/AssessmentSectionMergeHandlerTest.cs	(.../AssessmentSectionMergeHandlerTest.cs)	(revision 0a3fd57580aff0d6487e195c67f315f628b1ced4)
@@ -20,9 +20,13 @@
 // All rights reserved.
 
 using System;
+using System.Linq;
 using Core.Common.Gui.Commands;
 using NUnit.Framework;
 using Rhino.Mocks;
+using Ringtoets.Common.Data.AssessmentSection;
+using Ringtoets.Common.Data.FailureMechanism;
+using Ringtoets.Integration.Data;
 using Ringtoets.Integration.Plugin.Merge;
 
 namespace Ringtoets.Integration.Plugin.Test.Merge
@@ -56,5 +60,88 @@
             Assert.IsInstanceOf<IAssessmentSectionMergeHandler>(handler);
             mocks.VerifyAll();
         }
+
+        [Test]
+        public void PerformMerge_targetAssessmentSectionNull_ThrowsArgumentNullException()
+        {
+            // Setup
+            var mocks = new MockRepository();
+            var viewCommands = mocks.StrictMock<IViewCommands>();
+            mocks.ReplayAll();
+
+            var handler = new AssessmentSectionMergeHandler(viewCommands);
+
+            // Call
+            TestDelegate call = () => handler.PerformMerge(null, new AssessmentSection(AssessmentSectionComposition.Dike),
+                                                           Enumerable.Empty<IFailureMechanism>());
+
+            // Assert
+            var exception = Assert.Throws<ArgumentNullException>(call);
+            Assert.AreEqual("targetAssessmentSection", exception.ParamName);
+            mocks.VerifyAll();
+        }
+
+        [Test]
+        public void PerformMerge_sourceAssessmentSectionNull_ThrowsArgumentNullException()
+        {
+            // Setup
+            var mocks = new MockRepository();
+            var viewCommands = mocks.StrictMock<IViewCommands>();
+            mocks.ReplayAll();
+
+            var handler = new AssessmentSectionMergeHandler(viewCommands);
+
+            // Call
+            TestDelegate call = () => handler.PerformMerge(new AssessmentSection(AssessmentSectionComposition.Dike),
+                                                           null, Enumerable.Empty<IFailureMechanism>());
+
+            // Assert
+            var exception = Assert.Throws<ArgumentNullException>(call);
+            Assert.AreEqual("sourceAssessmentSection", exception.ParamName);
+            mocks.VerifyAll();
+        }
+
+        [Test]
+        public void PerformMerge_FailureMechanismsToMergeNull_ThrowsArgumentNullException()
+        {
+            // Setup
+            var mocks = new MockRepository();
+            var viewCommands = mocks.StrictMock<IViewCommands>();
+            mocks.ReplayAll();
+
+            var handler = new AssessmentSectionMergeHandler(viewCommands);
+
+            // Call
+            TestDelegate call = () => handler.PerformMerge(new AssessmentSection(AssessmentSectionComposition.Dike),
+                                                           new AssessmentSection(AssessmentSectionComposition.Dike),
+                                                           null);
+
+            // Assert
+            var exception = Assert.Throws<ArgumentNullException>(call);
+            Assert.AreEqual("failureMechanismsToMerge", exception.ParamName);
+            mocks.VerifyAll();
+        }
+
+        [Test]
+        public void PerformMerge_WithAllData_AllViewsForTargetAssessmentSectionClosed()
+        {
+            // Setup
+            var targetAssessmentSection = new AssessmentSection(AssessmentSectionComposition.Dike);
+
+            var mocks = new MockRepository();
+            var viewCommands = mocks.StrictMock<IViewCommands>();
+            viewCommands.Expect(vc => vc.RemoveAllViewsForItem(targetAssessmentSection));
+            mocks.ReplayAll();
+
+            var handler = new AssessmentSectionMergeHandler(viewCommands);
+
+            // Call
+            handler.PerformMerge(targetAssessmentSection,
+                                 new AssessmentSection(AssessmentSectionComposition.Dike),
+                                 Enumerable.Empty<IFailureMechanism>());
+
+            // Assert
+            mocks.VerifyAll();
+        }
     }
 }
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