Index: Ringtoets/Common/src/Ringtoets.Common.Forms/FailureMechanismPropertyChangeHandler.cs
===================================================================
diff -u -r9a001397536d9dcca5d009c8518478cdfcddbeca -r782c3e6bb64a0a674b33d6251b745dd71dade7bb
--- Ringtoets/Common/src/Ringtoets.Common.Forms/FailureMechanismPropertyChangeHandler.cs	(.../FailureMechanismPropertyChangeHandler.cs)	(revision 9a001397536d9dcca5d009c8518478cdfcddbeca)
+++ Ringtoets/Common/src/Ringtoets.Common.Forms/FailureMechanismPropertyChangeHandler.cs	(.../FailureMechanismPropertyChangeHandler.cs)	(revision 782c3e6bb64a0a674b33d6251b745dd71dade7bb)
@@ -1,4 +1,5 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using System.Linq;
 using System.Windows.Forms;
 using Core.Common.Base;
@@ -9,6 +10,10 @@
 
 namespace Ringtoets.Common.Forms
 {
+    /// <summary>
+    /// Class which properly handles data model changes due to a change of a
+    /// failure mechanism property.
+    /// </summary>
     public class FailureMechanismPropertyChangeHandler : IFailureMechanismPropertyChangeHandler
     {
         public bool ConfirmPropertyChange()
@@ -21,6 +26,10 @@
 
         public IEnumerable<IObservable> PropertyChanged(IFailureMechanism failureMechanism)
         {
+            if (failureMechanism == null)
+            {
+                throw new ArgumentNullException("failureMechanism");
+            }
             var affected = new List<IObservable>();
             foreach (var calculation in failureMechanism.Calculations.Where(c => c.HasOutput))
             {
Index: Ringtoets/Common/test/Ringtoets.Common.Forms.Test/FailureMechanismPropertyChangeHandlerTest.cs
===================================================================
diff -u
--- Ringtoets/Common/test/Ringtoets.Common.Forms.Test/FailureMechanismPropertyChangeHandlerTest.cs	(revision 0)
+++ Ringtoets/Common/test/Ringtoets.Common.Forms.Test/FailureMechanismPropertyChangeHandlerTest.cs	(revision 782c3e6bb64a0a674b33d6251b745dd71dade7bb)
@@ -0,0 +1,219 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using Core.Common.Base;
+using NUnit.Extensions.Forms;
+using NUnit.Framework;
+using Ringtoets.Common.Data;
+using Ringtoets.Common.Data.Calculation;
+using Ringtoets.Common.Data.FailureMechanism;
+using Ringtoets.Common.Data.TestUtil;
+
+namespace Ringtoets.Common.Forms.Test
+{
+    [TestFixture]
+    public class FailureMechanismPropertyChangeHandlerTest : NUnitFormTest
+    {
+        [Test]
+        public void ConfirmPropertyChange_Always_ShowMessageBox()
+        {
+            // Setup
+            string title = "";
+            string message = "";
+            DialogBoxHandler = (name, wnd) =>
+            {
+                var tester = new MessageBoxTester(wnd);
+                title = tester.Title;
+                message = tester.Text;
+
+                tester.ClickOk();
+            };
+
+            var handler = new FailureMechanismPropertyChangeHandler();
+
+            // Call
+            handler.ConfirmPropertyChange();
+
+            // Assert
+            Assert.AreEqual("Bevestigen", title);
+            string expectedMessage = "Als u een parameter in een toetsspoor wijzigt, zal de uitvoer van alle berekeningen in dit toetsspoor verwijderd worden." + Environment.NewLine +
+                                     Environment.NewLine +
+                                     "Weet u zeker dat u wilt doorgaan?";
+            Assert.AreEqual(expectedMessage, message);
+        }
+
+        [Test]
+        public void ConfirmPropertyChange_MessageBoxOk_ReturnTrue()
+        {
+            DialogBoxHandler = (name, wnd) =>
+            {
+                var tester = new MessageBoxTester(wnd);
+                tester.ClickOk();
+            };
+
+            var handler = new FailureMechanismPropertyChangeHandler();
+
+            // Call
+            bool result = handler.ConfirmPropertyChange();
+
+            // Assert
+            Assert.IsTrue(result);
+        }
+
+        [Test]
+        public void ConfirmPropertyChange_MessageBoxCancel_ReturnFalse()
+        {
+            DialogBoxHandler = (name, wnd) =>
+            {
+                var tester = new MessageBoxTester(wnd);
+                tester.ClickCancel();
+            };
+
+            var handler = new FailureMechanismPropertyChangeHandler();
+
+            // Call
+            bool result = handler.ConfirmPropertyChange();
+
+            // Assert
+            Assert.IsFalse(result);
+        }
+
+        [Test]
+        public void ChangeComposition_WithoutFailureMechanism_ThrowsArgumentNullException()
+        {
+            // Setup
+            var handler = new FailureMechanismPropertyChangeHandler();
+
+            // Call
+            TestDelegate test = () => handler.PropertyChanged(null);
+
+            // Assert
+            var paramName = Assert.Throws<ArgumentNullException>(test).ParamName;
+            Assert.AreEqual("failureMechanism", paramName);
+        }
+
+        [Test]
+        [TestCaseSource("ChangeCompositionTestCases")]
+        public void ChangeComposition_FailureMechanismWithDifferentCalculationCollections_ReturnsCalculationsWhichHadOutput(ChangeCompositionTestCase testCase)
+        {
+            // Setup
+            var handler = new FailureMechanismPropertyChangeHandler();
+            IFailureMechanism failureMechanism = new TestFailureMechanism(testCase.Calculations);
+
+            // Call
+            IEnumerable<IObservable> result = handler.PropertyChanged(failureMechanism);
+
+            // Assert
+            CollectionAssert.AreEquivalent(testCase.ExpectedAffectedCalculations, result);
+        }
+
+        public class ChangeCompositionTestCase
+        {
+            public ChangeCompositionTestCase(ICollection<TestCalculation> calculations)
+            {
+                Calculations = calculations;
+                ExpectedAffectedCalculations = calculations.Where(c => c.HasOutput).ToArray();
+            }
+
+            public ICollection<TestCalculation> Calculations { get; private set; }
+            public ICollection<TestCalculation> ExpectedAffectedCalculations { get; private set; }
+        }
+
+        static IEnumerable ChangeCompositionTestCases()
+        {
+            yield return new TestCaseData(
+                new ChangeCompositionTestCase(new[]
+                             {
+                                 CreateCalculationWithOutput()
+                             })
+            ).SetName("Single calculation with output");
+
+            yield return new TestCaseData(
+                new ChangeCompositionTestCase(new[]
+                             {
+                                 CreateCalculationWithoutOutput()
+                             })
+            ).SetName("Single calculation without output");
+
+            yield return new TestCaseData(
+                new ChangeCompositionTestCase(new[]
+                             {
+                                 CreateCalculationWithoutOutput(),
+                                 CreateCalculationWithoutOutput()
+                             })
+            ).SetName("Two calculations without output");
+
+            yield return new TestCaseData(
+                new ChangeCompositionTestCase(new[]
+                             {
+                                 CreateCalculationWithOutput(),
+                                 CreateCalculationWithoutOutput()
+                             })
+            ).SetName("Calculation without and calculation with output");
+
+            yield return new TestCaseData(
+                new ChangeCompositionTestCase(new[]
+                             {
+                                 CreateCalculationWithOutput(),
+                                 CreateCalculationWithOutput()
+                             })
+            ).SetName("Two calculations with output");
+
+            yield return new TestCaseData(
+                new ChangeCompositionTestCase(new[]
+                             {
+                                 CreateCalculationWithOutput(),
+                                 CreateCalculationWithOutput(),
+                                 CreateCalculationWithoutOutput()
+                             })
+            ).SetName("Two calculations with and one calculation without output");
+        }
+
+        private static TestCalculation CreateCalculationWithoutOutput()
+        {
+            return new TestCalculation();
+        }
+
+        private static TestCalculation CreateCalculationWithOutput()
+        {
+            return new TestCalculation
+            {
+                Output = new object()
+            };
+        }
+
+        #region Test classes
+
+        public class TestCalculation : Observable, ICalculation
+        {
+            /// <summary>
+            /// Gets or sets an object that represents some output of this calculation.
+            /// </summary>
+            public object Output { get; set; }
+
+            public bool HasOutput
+            {
+                get
+                {
+                    return Output != null;
+                }
+            }
+
+            public void ClearOutput()
+            {
+                Output = null;
+            }
+
+            #region Irrelevant for test
+
+            public string Name { get; set; }
+            public Comment Comments { get; }
+
+            #endregion
+        }
+
+        #endregion
+    }
+
+}
\ No newline at end of file
Index: Ringtoets/Common/test/Ringtoets.Common.Forms.Test/Ringtoets.Common.Forms.Test.csproj
===================================================================
diff -u -r586d097de0087256cb5cf3dda3a3c612721fee9c -r782c3e6bb64a0a674b33d6251b745dd71dade7bb
--- Ringtoets/Common/test/Ringtoets.Common.Forms.Test/Ringtoets.Common.Forms.Test.csproj	(.../Ringtoets.Common.Forms.Test.csproj)	(revision 586d097de0087256cb5cf3dda3a3c612721fee9c)
+++ Ringtoets/Common/test/Ringtoets.Common.Forms.Test/Ringtoets.Common.Forms.Test.csproj	(.../Ringtoets.Common.Forms.Test.csproj)	(revision 782c3e6bb64a0a674b33d6251b745dd71dade7bb)
@@ -63,6 +63,7 @@
     <Compile Include="..\..\..\..\Core\Common\src\Core.Common.Version\GlobalAssembly.cs">
       <Link>Properties\GlobalAssembly.cs</Link>
     </Compile>
+    <Compile Include="FailureMechanismPropertyChangeHandlerTest.cs" />
     <Compile Include="GuiServices\HydraulicBoundaryLocationCalculationGuiServiceTest.cs" />
     <Compile Include="Helpers\NamingHelperTest.cs" />
     <Compile Include="Helpers\ProbabilityFormattingHelperTest.cs" />