Index: test/Plugins/Wti/Wti.Calculation.Test/Piping/PipingCalculationExceptionTest.cs
===================================================================
diff -u
--- test/Plugins/Wti/Wti.Calculation.Test/Piping/PipingCalculationExceptionTest.cs	(revision 0)
+++ test/Plugins/Wti/Wti.Calculation.Test/Piping/PipingCalculationExceptionTest.cs	(revision 17ff1f55ba16c96a71a4476845340e38a9fce99f)
@@ -0,0 +1,52 @@
+using System;
+using NUnit.Framework;
+using Wti.Calculation.Piping;
+
+namespace Wti.Calculation.Test.Piping
+{
+    public class PipingCalculationExceptionTest
+    {
+        [Test]
+        public void DefaultConstructor_InnerExceptionNullAndMessageDefault()
+        {
+            // Setup
+            var expectedMessage = String.Format("Exception of type '{0}' was thrown.", typeof(PipingCalculationException).FullName);
+
+            // Call
+            var exception = new PipingCalculationException();
+
+            // Assert
+            Assert.IsNull(exception.InnerException);
+            Assert.AreEqual(expectedMessage, exception.Message);
+        }
+
+        [Test]
+        public void Constructor_WithCustomMessage_InnerExceptionNullAndMessageSetToCustom()
+        {
+            // Setup
+            var expectedMessage ="Some exception message";
+
+            // Call
+            var exception = new PipingCalculationException(expectedMessage);
+
+            // Assert
+            Assert.IsNull(exception.InnerException);
+            Assert.AreEqual(expectedMessage, exception.Message);
+        }
+
+        [Test]
+        public void Constructor_WithCustomMessageAndInnerException_InnerExceptionSetAndMessageSetToCustom()
+        {
+            // Setup
+            var expectedMessage = "Some exception message";
+            var expectedInnerException = new Exception();
+
+            // Call
+            var exception = new PipingCalculationException(expectedMessage, expectedInnerException);
+
+            // Assert
+            Assert.AreSame(expectedInnerException, exception.InnerException);
+            Assert.AreEqual(expectedMessage, exception.Message);
+        }
+    }
+}
\ No newline at end of file
Index: test/Plugins/Wti/Wti.Calculation.Test/Wti.Calculation.Test.csproj
===================================================================
diff -u -ra3b93c36c2051bd6112327bff0d836ae7883737d -r17ff1f55ba16c96a71a4476845340e38a9fce99f
--- test/Plugins/Wti/Wti.Calculation.Test/Wti.Calculation.Test.csproj	(.../Wti.Calculation.Test.csproj)	(revision a3b93c36c2051bd6112327bff0d836ae7883737d)
+++ test/Plugins/Wti/Wti.Calculation.Test/Wti.Calculation.Test.csproj	(.../Wti.Calculation.Test.csproj)	(revision 17ff1f55ba16c96a71a4476845340e38a9fce99f)
@@ -42,6 +42,7 @@
     <Reference Include="System.Core" />
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="Piping\PipingCalculationExceptionTest.cs" />
     <Compile Include="Piping\PipingCalculationInputTest.cs" />
     <Compile Include="Piping\PipingCalculationResultTest.cs" />
     <Compile Include="Piping\PipingCalculationTest.cs" />
Index: test/Plugins/Wti/Wti.Data.Test/PipingDataTest.cs
===================================================================
diff -u -ra8605fbec9c103f6b54775d479ec3c6078b484a2 -r17ff1f55ba16c96a71a4476845340e38a9fce99f
--- test/Plugins/Wti/Wti.Data.Test/PipingDataTest.cs	(.../PipingDataTest.cs)	(revision a8605fbec9c103f6b54775d479ec3c6078b484a2)
+++ test/Plugins/Wti/Wti.Data.Test/PipingDataTest.cs	(.../PipingDataTest.cs)	(revision 17ff1f55ba16c96a71a4476845340e38a9fce99f)
@@ -136,44 +136,5 @@
             // Call & Assert
             pipingData.Detach(observer);
         }
-
-        [Test]
-        public void Output_SetToNullWithListeners_ListenersNotified()
-        {
-            // Setup
-            var observer = mockRepository.StrictMock<IObserver>();
-            observer.Expect(o => o.UpdateObserver());
-            mockRepository.ReplayAll();
-
-            var pipingData = new PipingData();
-            pipingData.Attach(observer);
-
-            // Call & Assert
-            pipingData.Output = null;
-        }
-
-        [Test]
-        public void Output_SetToNewOutputWithListeners_ListenersNotified()
-        {
-            // Setup
-            var random = new Random(22);
-            var pipingData = new PipingData();
-
-            var observer = mockRepository.StrictMock<IObserver>();
-            observer.Expect(o => o.UpdateObserver());
-
-            pipingData.Attach(observer);
-            mockRepository.ReplayAll();
-
-            // Call & Assert
-            pipingData.Output = new PipingOutput(
-                random.NextDouble(),
-                random.NextDouble(),
-                random.NextDouble(),
-                random.NextDouble(),
-                random.NextDouble(),
-                random.NextDouble()
-            );
-        }
     }
 }
\ No newline at end of file
Index: test/Plugins/Wti/Wti.Data.Test/PipingFailureMechanismTest.cs
===================================================================
diff -u -rb16cc39381e4275844ad330e0bc56ede52aa5b88 -r17ff1f55ba16c96a71a4476845340e38a9fce99f
--- test/Plugins/Wti/Wti.Data.Test/PipingFailureMechanismTest.cs	(.../PipingFailureMechanismTest.cs)	(revision b16cc39381e4275844ad330e0bc56ede52aa5b88)
+++ test/Plugins/Wti/Wti.Data.Test/PipingFailureMechanismTest.cs	(.../PipingFailureMechanismTest.cs)	(revision 17ff1f55ba16c96a71a4476845340e38a9fce99f)
@@ -1,10 +1,20 @@
-using NUnit.Framework;
+using DelftTools.Shell.Core;
+using NUnit.Framework;
+using Rhino.Mocks;
 
 namespace Wti.Data.Test
 {
     [TestFixture]
     public class PipingFailureMechanismTest
     {
+        private MockRepository mockRepository;
+
+        [SetUp]
+        public void SetUp()
+        {
+            mockRepository = new MockRepository();
+        }
+
         [Test]
         public void DefaultConstructor_ExpectedValues()
         {
@@ -15,5 +25,94 @@
             CollectionAssert.IsEmpty(piping.SurfaceLines);
             Assert.IsNotNull(piping.PipingData);
         }
+
+        [Test]
+        public void Notify_SingleListenerAttached_ListenerIsNotified()
+        {
+            // Setup
+            var observer = mockRepository.StrictMock<IObserver>();
+            observer.Expect(o => o.UpdateObserver());
+
+            mockRepository.ReplayAll();
+
+            var pipingFailureMechanism = new PipingFailureMechanism();
+
+            pipingFailureMechanism.Attach(observer);
+
+            // Call & Assert
+            pipingFailureMechanism.NotifyObservers();
+        }
+
+        [Test]
+        public void Notify_SingleListenerAttachedAndDeattached_ListenerIsNotNotified()
+        {
+            // Setup
+            var observer = mockRepository.StrictMock<IObserver>();
+            observer.Expect(o => o.UpdateObserver()).Repeat.Never();
+            mockRepository.ReplayAll();
+
+            var pipingFailureMechanism = new PipingFailureMechanism();
+
+            pipingFailureMechanism.Attach(observer);
+            pipingFailureMechanism.Detach(observer);
+
+            // Call & Assert
+            pipingFailureMechanism.NotifyObservers();
+        }
+
+        [Test]
+        public void Notify_TwoListenersAttached_BothAreNotified()
+        {
+            // Setup
+            var observerA = mockRepository.StrictMock<IObserver>();
+            observerA.Expect(o => o.UpdateObserver());
+
+            var observerB = mockRepository.StrictMock<IObserver>();
+            observerB.Expect(o => o.UpdateObserver());
+
+            mockRepository.ReplayAll();
+
+            var pipingFailureMechanism = new PipingFailureMechanism();
+
+            pipingFailureMechanism.Attach(observerA);
+            pipingFailureMechanism.Attach(observerB);
+
+            // Call & Assert
+            pipingFailureMechanism.NotifyObservers();
+        }
+
+        [Test]
+        public void Notify_TwoListenersAttachedOneDetached_InvokedOnce()
+        {
+            // Setup
+            var observerA = mockRepository.StrictMock<IObserver>();
+            observerA.Expect(o => o.UpdateObserver()).Repeat.Never();
+
+            var observerB = mockRepository.StrictMock<IObserver>();
+            observerB.Expect(o => o.UpdateObserver());
+
+            mockRepository.ReplayAll();
+
+            var pipingFailureMechanism = new PipingFailureMechanism();
+
+            pipingFailureMechanism.Attach(observerA);
+            pipingFailureMechanism.Attach(observerB);
+            pipingFailureMechanism.Detach(observerA);
+
+            // Call & Assert
+            pipingFailureMechanism.NotifyObservers();
+        }
+
+        [Test]
+        public void Detach_DetachNonAttachedObserver_ThrowsNoException()
+        {
+            // Setup
+            var observer = mockRepository.StrictMock<IObserver>();
+
+            var pipingFailureMechanism = new PipingFailureMechanism();
+
+            // Call & Assert
+            pipingFailureMechanism.Detach(observer);
+        }
     }
 }
\ No newline at end of file