SEBWIN-221: Fixed issues with the operation model by separating repeatable from non-repeatable operations and solved conundrum with session operation sequence.

SafeExamBrowser.Client.UnitTests/Operations/BrowserOperationTests.cs

@@ -6,7 +6,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-using System;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Moq;
 using SafeExamBrowser.Client.Operations;
@@ -64,12 +63,5 @@ namespace SafeExamBrowser.Client.UnitTests.Operations
 
 			controllerMock.Verify(c => c.Terminate(), Times.Once);
 		}
-
-		[TestMethod]
-		[ExpectedException(typeof(InvalidOperationException))]
-		public void MustNotAllowRepeating()
-		{
-			sut.Repeat();
-		}
 	}
 }

SafeExamBrowser.Client.UnitTests/Operations/ClientHostDisconnectionOperationTests.cs

@@ -96,12 +96,5 @@ namespace SafeExamBrowser.Client.UnitTests.Operations
 
 			Assert.AreEqual(OperationResult.Success, result);
 		}
-
-		[TestMethod]
-		[ExpectedException(typeof(InvalidOperationException))]
-		public void MustNotAllowRepeating()
-		{
-			sut.Repeat();
-		}
 	}
 }

SafeExamBrowser.Client.UnitTests/Operations/ClipboardOperationTests.cs

@@ -6,7 +6,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-using System;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Moq;
 using SafeExamBrowser.Client.Operations;
@@ -47,12 +46,5 @@ namespace SafeExamBrowser.Client.UnitTests.Operations
 
 			nativeMethodsMock.Verify(n => n.EmptyClipboard(), Times.Once);
 		}
-
-		[TestMethod]
-		[ExpectedException(typeof(InvalidOperationException))]
-		public void MustNotAllowRepeating()
-		{
-			sut.Repeat();
-		}
 	}
 }

SafeExamBrowser.Client.UnitTests/Operations/ConfigurationOperationTests.cs

@@ -6,7 +6,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-using System;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Moq;
 using SafeExamBrowser.Client.Operations;
@@ -39,12 +38,5 @@ namespace SafeExamBrowser.Client.UnitTests.Operations
 		{
 			Assert.Fail();
 		}
-
-		[TestMethod]
-		[ExpectedException(typeof(InvalidOperationException))]
-		public void MustNotAllowRepeating()
-		{
-			sut.Repeat();
-		}
 	}
 }

SafeExamBrowser.Client.UnitTests/Operations/DisplayMonitorOperationTests.cs

@@ -6,7 +6,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-using System;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Moq;
 using SafeExamBrowser.Client.Operations;
@@ -64,12 +63,5 @@ namespace SafeExamBrowser.Client.UnitTests.Operations
 			displayMonitorMock.Verify(d => d.StopMonitoringDisplayChanges(), Times.Once);
 			displayMonitorMock.Verify(d => d.ResetPrimaryDisplay(), Times.Once);
 		}
-
-		[TestMethod]
-		[ExpectedException(typeof(InvalidOperationException))]
-		public void MustNotAllowRepeating()
-		{
-			sut.Repeat();
-		}
 	}
 }

SafeExamBrowser.Client.UnitTests/Operations/KeyboardInterceptorOperationTests.cs

@@ -6,7 +6,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-using System;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Moq;
 using SafeExamBrowser.Client.Operations;
@@ -50,12 +49,5 @@ namespace SafeExamBrowser.Client.UnitTests.Operations
 
 			nativeMethodsMock.Verify(n => n.DeregisterKeyboardHook(It.IsAny<IKeyboardInterceptor>()), Times.Once);
 		}
-
-		[TestMethod]
-		[ExpectedException(typeof(InvalidOperationException))]
-		public void MustNotAllowRepeating()
-		{
-			sut.Repeat();
-		}
 	}
 }

SafeExamBrowser.Client.UnitTests/Operations/MouseInterceptorOperationTests.cs

@@ -6,7 +6,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-using System;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Moq;
 using SafeExamBrowser.Client.Operations;
@@ -50,12 +49,5 @@ namespace SafeExamBrowser.Client.UnitTests.Operations
 
 			nativeMethodsMock.Verify(n => n.DeregisterMouseHook(It.IsAny<IMouseInterceptor>()), Times.Once);
 		}
-
-		[TestMethod]
-		[ExpectedException(typeof(InvalidOperationException))]
-		public void MustNotAllowRepeating()
-		{
-			sut.Repeat();
-		}
 	}
 }

SafeExamBrowser.Client.UnitTests/Operations/ProcessMonitorOperationTests.cs

@@ -6,7 +6,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-using System;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Moq;
 using SafeExamBrowser.Client.Operations;
@@ -71,12 +70,5 @@ namespace SafeExamBrowser.Client.UnitTests.Operations
 			processMonitor.Verify(p => p.StartMonitoringExplorer(), Times.Never);
 			processMonitor.Verify(p => p.StopMonitoringExplorer(), Times.Never);
 		}
-
-		[TestMethod]
-		[ExpectedException(typeof(InvalidOperationException))]
-		public void MustNotAllowRepeating()
-		{
-			sut.Repeat();
-		}
 	}
 }

SafeExamBrowser.Client.UnitTests/Operations/RuntimeConnectionOperationTests.cs

@@ -6,10 +6,8 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-using System;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Moq;
-using SafeExamBrowser.Client.Operations;
 using SafeExamBrowser.Contracts.Communication.Proxies;
 using SafeExamBrowser.Contracts.Logging;
 
@@ -33,14 +31,5 @@ namespace SafeExamBrowser.Client.UnitTests.Operations
 		{
 			Assert.Fail();
 		}
-
-		[TestMethod]
-		[ExpectedException(typeof(InvalidOperationException))]
-		public void MustNotAllowRepeating()
-		{
-			var sut = new RuntimeConnectionOperation(logger.Object, runtime.Object, Guid.Empty);
-
-			sut.Repeat();
-		}
 	}
 }

SafeExamBrowser.Client.UnitTests/Operations/TaskbarOperationTests.cs

@@ -6,7 +6,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-using System;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Moq;
 using SafeExamBrowser.Client.Operations;
@@ -94,12 +93,5 @@ namespace SafeExamBrowser.Client.UnitTests.Operations
 			powerSupplyMock.Verify(p => p.Terminate(), Times.Once);
 			wirelessNetworkMock.Verify(w => w.Terminate(), Times.Once);
 		}
-
-		[TestMethod]
-		[ExpectedException(typeof(InvalidOperationException))]
-		public void MustNotAllowRepeating()
-		{
-			sut.Repeat();
-		}
 	}
 }

SafeExamBrowser.Client.UnitTests/Operations/WindowMonitorOperationTests.cs

@@ -6,7 +6,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-using System;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Moq;
 using SafeExamBrowser.Client.Operations;
@@ -106,14 +105,5 @@ namespace SafeExamBrowser.Client.UnitTests.Operations
 
 			windowMonitorMock.VerifyNoOtherCalls();
 		}
-
-		[TestMethod]
-		[ExpectedException(typeof(InvalidOperationException))]
-		public void MustNotAllowRepeating()
-		{
-			var sut = new WindowMonitorOperation(KioskMode.None, loggerMock.Object, windowMonitorMock.Object);
-
-			sut.Repeat();
-		}
 	}
 }

SafeExamBrowser.Client/ClientController.cs

@@ -140,7 +140,7 @@ namespace SafeExamBrowser.Client
 
 			DeregisterEvents();
 
-			var success = operations.TryRevert();
+			var success = operations.TryRevert() == OperationResult.Success;
 
 			if (success)
 			{

SafeExamBrowser.Client/Operations/BrowserOperation.cs

@@ -6,7 +6,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-using System;
 using SafeExamBrowser.Contracts.Configuration;
 using SafeExamBrowser.Contracts.Core;
 using SafeExamBrowser.Contracts.Core.OperationModel;
@@ -58,17 +57,14 @@ namespace SafeExamBrowser.Client.Operations
 			return OperationResult.Success;
 		}
 
-		public OperationResult Repeat()
+		public OperationResult Revert()
-		{
-			throw new InvalidOperationException($"The '{nameof(BrowserOperation)}' is not meant to be repeated!");
-		}
-
-		public void Revert()
 		{
 			logger.Info("Terminating browser...");
 			StatusChanged?.Invoke(TextKey.OperationStatus_TerminateBrowser);
 
 			browserController.Terminate();
+
+			return OperationResult.Success;
 		}
 	}
 }

SafeExamBrowser.Client/Operations/ClientHostDisconnectionOperation.cs

@@ -6,7 +6,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-using System;
 using System.Threading;
 using SafeExamBrowser.Contracts.Communication.Events;
 using SafeExamBrowser.Contracts.Communication.Hosts;
@@ -42,29 +41,32 @@ namespace SafeExamBrowser.Client.Operations
 			return OperationResult.Success;
 		}
 
-		public OperationResult Repeat()
+		public OperationResult Revert()
 		{
-			throw new InvalidOperationException($"The '{nameof(ClientHostDisconnectionOperation)}' is not meant to be repeated!");
+			StatusChanged?.Invoke(TextKey.OperationStatus_WaitRuntimeDisconnection);
-		}
 
-		public void Revert()
+			if (clientHost.IsConnected)
 			{
 				var disconnected = false;
 				var disconnectedEvent = new AutoResetEvent(false);
 				var disconnectedEventHandler = new CommunicationEventHandler(() => disconnectedEvent.Set());
 
-			StatusChanged?.Invoke(TextKey.OperationStatus_WaitRuntimeDisconnection);
-
 				clientHost.RuntimeDisconnected += disconnectedEventHandler;
 
-			if (clientHost.IsConnected)
-			{
 				logger.Info("Waiting for runtime to disconnect from client communication host...");
 				disconnected = disconnectedEvent.WaitOne(timeout_ms);
 
-				if (!disconnected)
+				clientHost.RuntimeDisconnected -= disconnectedEventHandler;
+
+				if (disconnected)
 				{
-					logger.Error($"Runtime failed to disconnect within {timeout_ms / 1000} seconds!");
+					logger.Info("The runtime has successfully disconnected from the client communication host.");
+				}
+				else
+				{
+					logger.Error($"The runtime failed to disconnect within {timeout_ms / 1000} seconds!");
+
+					return OperationResult.Failed;
 				}
 			}
 			else
@@ -72,7 +74,7 @@ namespace SafeExamBrowser.Client.Operations
 				logger.Info("The runtime has already disconnected from the client communication host.");
 			}
 
-			clientHost.RuntimeDisconnected -= disconnectedEventHandler;
+			return OperationResult.Success;
 		}
 	}
 }

SafeExamBrowser.Client/Operations/ClipboardOperation.cs

@@ -6,7 +6,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-using System;
 using SafeExamBrowser.Contracts.Core.OperationModel;
 using SafeExamBrowser.Contracts.Core.OperationModel.Events;
 using SafeExamBrowser.Contracts.I18n;
@@ -36,14 +35,11 @@ namespace SafeExamBrowser.Client.Operations
 			return OperationResult.Success;
 		}
 
-		public OperationResult Repeat()
+		public OperationResult Revert()
-		{
-			throw new InvalidOperationException($"The '{nameof(ClipboardOperation)}' is not meant to be repeated!");
-		}
-
-		public void Revert()
 		{
 			EmptyClipboard();
+
+			return OperationResult.Success;
 		}
 
 		private void EmptyClipboard()

SafeExamBrowser.Client/Operations/ConfigurationOperation.cs

@@ -61,14 +61,9 @@ namespace SafeExamBrowser.Client.Operations
 			return OperationResult.Success;
 		}
 
-		public OperationResult Repeat()
+		public OperationResult Revert()
 		{
-			throw new InvalidOperationException($"The '{nameof(ConfigurationOperation)}' is not meant to be repeated!");
+			return OperationResult.Success;
-		}
-
-		public void Revert()
-		{
-			// Nothing to do here...
 		}
 	}
 }

SafeExamBrowser.Client/Operations/DisplayMonitorOperation.cs

@@ -6,7 +6,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-using System;
 using SafeExamBrowser.Contracts.Core.OperationModel;
 using SafeExamBrowser.Contracts.Core.OperationModel.Events;
 using SafeExamBrowser.Contracts.I18n;
@@ -44,18 +43,15 @@ namespace SafeExamBrowser.Client.Operations
 			return OperationResult.Success;
 		}
 
-		public OperationResult Repeat()
+		public OperationResult Revert()
-		{
-			throw new InvalidOperationException($"The '{nameof(DisplayMonitorOperation)}' is not meant to be repeated!");
-		}
-
-		public void Revert()
 		{
 			logger.Info("Restoring working area...");
 			StatusChanged?.Invoke(TextKey.OperationStatus_RestoreWorkingArea);
 
 			displayMonitor.StopMonitoringDisplayChanges();
 			displayMonitor.ResetPrimaryDisplay();
+
+			return OperationResult.Success;
 		}
 	}
 }

SafeExamBrowser.Client/Operations/KeyboardInterceptorOperation.cs

@@ -6,7 +6,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-using System;
 using SafeExamBrowser.Contracts.Core.OperationModel;
 using SafeExamBrowser.Contracts.Core.OperationModel.Events;
 using SafeExamBrowser.Contracts.I18n;
@@ -45,17 +44,14 @@ namespace SafeExamBrowser.Client.Operations
 			return OperationResult.Success;
 		}
 
-		public OperationResult Repeat()
+		public OperationResult Revert()
-		{
-			throw new InvalidOperationException($"The '{nameof(KeyboardInterceptorOperation)}' is not meant to be repeated!");
-		}
-
-		public void Revert()
 		{
 			logger.Info("Stopping keyboard interception...");
 			StatusChanged?.Invoke(TextKey.OperationStatus_StopKeyboardInterception);
 
 			nativeMethods.DeregisterKeyboardHook(keyboardInterceptor);
+
+			return OperationResult.Success;
 		}
 	}
 }

SafeExamBrowser.Client/Operations/MouseInterceptorOperation.cs

@@ -6,7 +6,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-using System;
 using SafeExamBrowser.Contracts.Core.OperationModel;
 using SafeExamBrowser.Contracts.Core.OperationModel.Events;
 using SafeExamBrowser.Contracts.I18n;
@@ -45,17 +44,14 @@ namespace SafeExamBrowser.Client.Operations
 			return OperationResult.Success;
 		}
 
-		public OperationResult Repeat()
+		public OperationResult Revert()
-		{
-			throw new InvalidOperationException($"The '{nameof(MouseInterceptorOperation)}' is not meant to be repeated!");
-		}
-
-		public void Revert()
 		{
 			logger.Info("Stopping mouse interception...");
 			StatusChanged?.Invoke(TextKey.OperationStatus_StopMouseInterception);
 
 			nativeMethods.DeregisterMouseHook(mouseInterceptor);
+
+			return OperationResult.Success;
 		}
 	}
 }

SafeExamBrowser.Client/Operations/ProcessMonitorOperation.cs

@@ -6,7 +6,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-using System;
 using SafeExamBrowser.Contracts.Configuration.Settings;
 using SafeExamBrowser.Contracts.Core.OperationModel;
 using SafeExamBrowser.Contracts.Core.OperationModel.Events;
@@ -45,12 +44,7 @@ namespace SafeExamBrowser.Client.Operations
 			return OperationResult.Success;
 		}
 
-		public OperationResult Repeat()
+		public OperationResult Revert()
-		{
-			throw new InvalidOperationException($"The '{nameof(ProcessMonitorOperation)}' is not meant to be repeated!");
-		}
-
-		public void Revert()
 		{
 			logger.Info("Stopping process monitoring...");
 			StatusChanged?.Invoke(TextKey.OperationStatus_StopProcessMonitoring);
@@ -59,6 +53,8 @@ namespace SafeExamBrowser.Client.Operations
 			{
 				processMonitor.StopMonitoringExplorer();
 			}
+
+			return OperationResult.Success;
 		}
 	}
 }

SafeExamBrowser.Client/Operations/RuntimeConnectionOperation.cs

@@ -51,12 +51,7 @@ namespace SafeExamBrowser.Client.Operations
 			return connected ? OperationResult.Success : OperationResult.Failed;
 		}
 
-		public OperationResult Repeat()
+		public OperationResult Revert()
-		{
-			throw new InvalidOperationException($"The '{nameof(RuntimeConnectionOperation)}' is not meant to be repeated!");
-		}
-
-		public void Revert()
 		{
 			logger.Info("Closing runtime connection...");
 			StatusChanged?.Invoke(TextKey.OperationStatus_CloseRuntimeConnection);
@@ -73,7 +68,11 @@ namespace SafeExamBrowser.Client.Operations
 				{
 					logger.Error("Failed to disconnect from the runtime!");
 				}
-			}
+
+				return success ? OperationResult.Success : OperationResult.Failed;
+			}
+
+			return OperationResult.Success;
 		}
 	}
 }

SafeExamBrowser.Client/Operations/TaskbarOperation.cs

@@ -6,7 +6,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-using System;
 using SafeExamBrowser.Contracts.Configuration;
 using SafeExamBrowser.Contracts.Configuration.Settings;
 using SafeExamBrowser.Contracts.Core;
@@ -91,12 +90,7 @@ namespace SafeExamBrowser.Client.Operations
 			return OperationResult.Success;
 		}
 
-		public OperationResult Repeat()
+		public OperationResult Revert()
-		{
-			throw new InvalidOperationException($"The '{nameof(TaskbarOperation)}' is not meant to be repeated!");
-		}
-
-		public void Revert()
 		{
 			logger.Info("Terminating taskbar...");
 			StatusChanged?.Invoke(TextKey.OperationStatus_TerminateTaskbar);
@@ -120,6 +114,8 @@ namespace SafeExamBrowser.Client.Operations
 			{
 				wirelessNetwork.Terminate();
 			}
+
+			return OperationResult.Success;
 		}
 
 		private void AddKeyboardLayoutControl()

SafeExamBrowser.Client/Operations/WindowMonitorOperation.cs

@@ -6,7 +6,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-using System;
 using SafeExamBrowser.Contracts.Configuration.Settings;
 using SafeExamBrowser.Contracts.Core.OperationModel;
 using SafeExamBrowser.Contracts.Core.OperationModel.Events;
@@ -50,12 +49,7 @@ namespace SafeExamBrowser.Client.Operations
 			return OperationResult.Success;
 		}
 
-		public OperationResult Repeat()
+		public OperationResult Revert()
-		{
-			throw new InvalidOperationException($"The '{nameof(WindowMonitorOperation)}' is not meant to be repeated!");
-		}
-
-		public void Revert()
 		{
 			logger.Info("Stopping window monitoring...");
 			StatusChanged?.Invoke(TextKey.OperationStatus_StopWindowMonitoring);
@@ -69,6 +63,8 @@ namespace SafeExamBrowser.Client.Operations
 			{
 				windowMonitor.RestoreHiddenWindows();
 			}
+
+			return OperationResult.Success;
 		}
 	}
 }

SafeExamBrowser.Configuration/ConfigurationRepository.cs

@@ -64,9 +64,9 @@ namespace SafeExamBrowser.Configuration
 		{
 			CurrentSession = new SessionData
 			{
-				ClientProcess = CurrentSession?.ClientProcess,
-				ClientProxy = CurrentSession?.ClientProxy,
 				Id = Guid.NewGuid(),
+				NewDesktop = CurrentSession?.NewDesktop,
+				OriginalDesktop = CurrentSession?.OriginalDesktop,
 				StartupToken = Guid.NewGuid()
 			};
 

SafeExamBrowser.Configuration/SessionData.cs

@@ -18,6 +18,8 @@ namespace SafeExamBrowser.Configuration
 		public IClientProxy ClientProxy { get; set; }
 		public IProcess ClientProcess { get; set; }
 		public Guid Id { get; set; }
+		public IDesktop NewDesktop { get; set; }
+		public IDesktop OriginalDesktop { get; set; }
 		public Guid StartupToken { get; set; }
 	}
 }

SafeExamBrowser.Contracts/Configuration/ISessionData.cs

@@ -13,7 +13,7 @@ using SafeExamBrowser.Contracts.WindowsApi;
 namespace SafeExamBrowser.Contracts.Configuration
 {
 	/// <summary>
-	/// Defines all session-related (configuration) data.
+	/// Holds all session-related configuration and runtime data.
 	/// </summary>
 	public interface ISessionData
 	{
@@ -32,6 +32,16 @@ namespace SafeExamBrowser.Contracts.Configuration
 		/// </summary>
 		Guid Id { get; }
 
+		/// <summary>
+		/// The new desktop, if <see cref="Settings.KioskMode.CreateNewDesktop"/> is active for this session.
+		/// </summary>
+		IDesktop NewDesktop { get; set; }
+
+		/// <summary>
+		/// The original desktop, if <see cref="Settings.KioskMode.CreateNewDesktop"/> is active for this session.
+		/// </summary>
+		IDesktop OriginalDesktop { get; set; }
+
 		/// <summary>
 		/// The startup token used by the client and runtime components for initial authentication.
 		/// </summary>

SafeExamBrowser.Contracts/Core/OperationModel/IOperation.cs

@@ -31,13 +31,8 @@ namespace SafeExamBrowser.Contracts.Core.OperationModel
 		OperationResult Perform();
 
 		/// <summary>
-		/// Repeats the operation.
+		/// Reverts all changes made when executing the operation.
 		/// </summary>
-		OperationResult Repeat();
+		OperationResult Revert();
-
-		/// <summary>
-		/// Reverts all changes which were made when executing the operation.
-		/// </summary>
-		void Revert();
 	}
 }

SafeExamBrowser.Contracts/Core/OperationModel/IOperationSequence.cs

@@ -11,14 +11,13 @@ using SafeExamBrowser.Contracts.Core.OperationModel.Events;
 namespace SafeExamBrowser.Contracts.Core.OperationModel
 {
 	/// <summary>
-	/// A sequence of <see cref="IOperation"/>s which can be used for sequential procedures, e.g. the initialization &amp; finalization of
+	/// A sequence of <see cref="IOperation"/> which can be used for sequential procedures, e.g. the initialization &amp; finalization of
 	/// an application component. Each operation will be executed failsafe, i.e. the return value will indicate whether a procedure
 	/// completed successfully or not.
 	/// 
 	/// Exemplary execution order for a sequence initialized with operations A, B, C, D:
 	/// 
 	/// <see cref="TryPerform"/>: A -> B -> C -> D.
-	/// <see cref="TryRepeat"/>: A -> B -> C -> D.
 	/// <see cref="TryRevert"/>: D -> C -> B -> A.
 	/// </summary>
 	public interface IOperationSequence
@@ -45,15 +44,9 @@ namespace SafeExamBrowser.Contracts.Core.OperationModel
 		OperationResult TryPerform();
 
 		/// <summary>
-		/// Tries to repeat the operations of this sequence according to their initialized order. If any operation fails, the already
+		/// Tries to revert the operations of this sequence in reversion of their initialized order. The reversion of all operations will
-		/// performed operations will not be reverted.
+		/// continue, even if one or multiple operations fail to revert successfully.
 		/// </summary>
-		OperationResult TryRepeat();
+		OperationResult TryRevert();
-
-		/// <summary>
-		/// Tries to revert the operations of this sequence. Returns <c>true</c> if all operations were reverted without errors,
-		/// otherwise <c>false</c>. The reversion of all operations will continue, even if one or multiple operations fail.
-		/// </summary>
-		bool TryRevert();
 	}
 }

SafeExamBrowser.Contracts/Core/OperationModel/IRepeatableOperation.cs

@@ -0,0 +1,21 @@
+/*
+ * Copyright (c) 2018 ETH Zürich, Educational Development and Technology (LET)
+ * 
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+namespace SafeExamBrowser.Contracts.Core.OperationModel
+{
+	/// <summary>
+	/// Defines an operation which can be executed multiple times as part of an <see cref="IRepeatableOperationSequence"/>.
+	/// </summary>
+	public interface IRepeatableOperation : IOperation
+	{
+		/// <summary>
+		/// Repeats the operation.
+		/// </summary>
+		OperationResult Repeat();
+	}
+}

SafeExamBrowser.Contracts/Core/OperationModel/IRepeatableOperationSequence.cs

@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2018 ETH Zürich, Educational Development and Technology (LET)
+ * 
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+namespace SafeExamBrowser.Contracts.Core.OperationModel
+{
+	/// <summary>
+	/// A sequence of <see cref="IRepeatableOperation"/> which can be used for repeatable sequential procedures.
+	/// 
+	/// Exemplary execution order for a sequence initialized with operations A, B, C, D:
+	/// 
+	/// <see cref="TryRepeat()"/>: A -> B -> C -> D.
+	/// </summary>
+	public interface IRepeatableOperationSequence : IOperationSequence
+	{
+		/// <summary>
+		/// Tries to repeat the operations of this sequence according to their initialized order. If any operation fails, the already
+		/// repeated operations will not be reverted.
+		/// </summary>
+		OperationResult TryRepeat();
+	}
+}

SafeExamBrowser.Contracts/Core/OperationModel/OperationResult.cs

@@ -9,7 +9,7 @@
 namespace SafeExamBrowser.Contracts.Core.OperationModel
 {
 	/// <summary>
-	/// Defines the result of the sequential execution of <see cref="IOperation"/>s (as part of an <see cref="IOperationSequence"/>).
+	/// Defines the operation result of the execution of an <see cref="IOperation"/> resp. <see cref="IOperationSequence"/>.
 	/// </summary>
 	public enum OperationResult
 	{

SafeExamBrowser.Contracts/SafeExamBrowser.Contracts.csproj

@@ -63,6 +63,8 @@
     <Compile Include="Core\OperationModel\Events\ProgressChangedEventHandler.cs" />
     <Compile Include="Core\OperationModel\Events\StatusChangedEventHandler.cs" />
     <Compile Include="Core\OperationModel\IOperationSequence.cs" />
+    <Compile Include="Core\OperationModel\IRepeatableOperation.cs" />
+    <Compile Include="Core\OperationModel\IRepeatableOperationSequence.cs" />
     <Compile Include="Core\OperationModel\OperationResult.cs" />
     <Compile Include="Browser\DownloadEventArgs.cs" />
     <Compile Include="Browser\DownloadFinishedCallback.cs" />

SafeExamBrowser.Core.UnitTests/OperationModel/OperationSequenceTests.cs

@@ -303,159 +303,6 @@ namespace SafeExamBrowser.Core.UnitTests.OperationModel
 
 		#endregion
 
-		#region Repeat Tests
-
-		[TestMethod]
-		public void MustCorrectlyAbortRepeat()
-		{
-			var operationA = new Mock<IOperation>();
-			var operationB = new Mock<IOperation>();
-			var operationC = new Mock<IOperation>();
-			var operations = new Queue<IOperation>();
-
-			operationA.Setup(o => o.Repeat()).Returns(OperationResult.Success);
-			operationB.Setup(o => o.Repeat()).Returns(OperationResult.Aborted);
-
-			operations.Enqueue(operationA.Object);
-			operations.Enqueue(operationB.Object);
-			operations.Enqueue(operationC.Object);
-
-			var sut = new OperationSequence(loggerMock.Object, operations);
-			var result = sut.TryRepeat();
-
-			operationA.Verify(o => o.Repeat(), Times.Once);
-			operationA.Verify(o => o.Revert(), Times.Never);
-			operationB.Verify(o => o.Repeat(), Times.Once);
-			operationB.Verify(o => o.Revert(), Times.Never);
-			operationC.Verify(o => o.Repeat(), Times.Never);
-			operationC.Verify(o => o.Revert(), Times.Never);
-
-			Assert.AreEqual(OperationResult.Aborted, result);
-		}
-
-		[TestMethod]
-		public void MustRepeatOperations()
-		{
-			var operationA = new Mock<IOperation>();
-			var operationB = new Mock<IOperation>();
-			var operationC = new Mock<IOperation>();
-			var operations = new Queue<IOperation>();
-
-			operationA.Setup(o => o.Repeat()).Returns(OperationResult.Success);
-			operationB.Setup(o => o.Repeat()).Returns(OperationResult.Success);
-			operationC.Setup(o => o.Repeat()).Returns(OperationResult.Success);
-
-			operations.Enqueue(operationA.Object);
-			operations.Enqueue(operationB.Object);
-			operations.Enqueue(operationC.Object);
-
-			var sut = new OperationSequence(loggerMock.Object, operations);
-			var result = sut.TryRepeat();
-
-			operationA.Verify(o => o.Perform(), Times.Never);
-			operationA.Verify(o => o.Repeat(), Times.Once);
-			operationA.Verify(o => o.Revert(), Times.Never);
-			operationB.Verify(o => o.Perform(), Times.Never);
-			operationB.Verify(o => o.Repeat(), Times.Once);
-			operationB.Verify(o => o.Revert(), Times.Never);
-			operationC.Verify(o => o.Perform(), Times.Never);
-			operationC.Verify(o => o.Repeat(), Times.Once);
-			operationC.Verify(o => o.Revert(), Times.Never);
-
-			Assert.AreEqual(OperationResult.Success, result);
-		}
-
-		[TestMethod]
-		public void MustRepeatOperationsInSequence()
-		{
-			int current = 0, a = 0, b = 0, c = 0;
-			var operationA = new Mock<IOperation>();
-			var operationB = new Mock<IOperation>();
-			var operationC = new Mock<IOperation>();
-			var operations = new Queue<IOperation>();
-
-			operationA.Setup(o => o.Repeat()).Returns(OperationResult.Success).Callback(() => a = ++current);
-			operationB.Setup(o => o.Repeat()).Returns(OperationResult.Success).Callback(() => b = ++current);
-			operationC.Setup(o => o.Repeat()).Returns(OperationResult.Success).Callback(() => c = ++current);
-
-			operations.Enqueue(operationA.Object);
-			operations.Enqueue(operationB.Object);
-			operations.Enqueue(operationC.Object);
-
-			var sut = new OperationSequence(loggerMock.Object, operations);
-			var result = sut.TryRepeat();
-
-			Assert.AreEqual(OperationResult.Success, result);
-			Assert.IsTrue(a == 1);
-			Assert.IsTrue(b == 2);
-			Assert.IsTrue(c == 3);
-		}
-
-		[TestMethod]
-		public void MustNotRevertOperationsInCaseOfError()
-		{
-			var operationA = new Mock<IOperation>();
-			var operationB = new Mock<IOperation>();
-			var operationC = new Mock<IOperation>();
-			var operationD = new Mock<IOperation>();
-			var operations = new Queue<IOperation>();
-
-			operationA.Setup(o => o.Repeat()).Returns(OperationResult.Success);
-			operationB.Setup(o => o.Repeat()).Returns(OperationResult.Success);
-			operationC.Setup(o => o.Repeat()).Throws<Exception>();
-
-			operations.Enqueue(operationA.Object);
-			operations.Enqueue(operationB.Object);
-			operations.Enqueue(operationC.Object);
-			operations.Enqueue(operationD.Object);
-
-			var sut = new OperationSequence(loggerMock.Object, operations);
-			var result = sut.TryRepeat();
-
-			operationA.Verify(o => o.Repeat(), Times.Once);
-			operationA.Verify(o => o.Revert(), Times.Never);
-			operationB.Verify(o => o.Repeat(), Times.Once);
-			operationB.Verify(o => o.Revert(), Times.Never);
-			operationC.Verify(o => o.Repeat(), Times.Once);
-			operationC.Verify(o => o.Revert(), Times.Never);
-			operationD.Verify(o => o.Repeat(), Times.Never);
-			operationD.Verify(o => o.Revert(), Times.Never);
-
-			Assert.AreEqual(OperationResult.Failed, result);
-		}
-
-		[TestMethod]
-		public void MustSucceedRepeatingWithEmptyQueue()
-		{
-			var sut = new OperationSequence(loggerMock.Object, new Queue<IOperation>());
-			var result = sut.TryRepeat();
-
-			Assert.AreEqual(OperationResult.Success, result);
-		}
-
-		[TestMethod]
-		public void MustSucceedRepeatingWithoutCallingPerform()
-		{
-			var sut = new OperationSequence(loggerMock.Object, new Queue<IOperation>());
-			var result = sut.TryRepeat();
-
-			Assert.AreEqual(OperationResult.Success, result);
-		}
-
-		[TestMethod]
-		public void MustNotFailInCaseOfUnexpectedErrorWhenRepeating()
-		{
-			var sut = new OperationSequence(loggerMock.Object, new Queue<IOperation>());
-
-			sut.ProgressChanged += (args) => throw new Exception();
-
-			var result = sut.TryRepeat();
-
-			Assert.AreEqual(OperationResult.Failed, result);
-		}
-
-		#endregion
-
 		#region Revert Tests
 
 		[TestMethod]
@@ -467,11 +314,11 @@ namespace SafeExamBrowser.Core.UnitTests.OperationModel
 			var operations = new Queue<IOperation>();
 
 			operationA.Setup(o => o.Perform()).Returns(OperationResult.Success);
-			operationA.Setup(o => o.Repeat()).Returns(OperationResult.Success);
+			operationA.Setup(o => o.Revert()).Returns(OperationResult.Success);
 			operationB.Setup(o => o.Perform()).Returns(OperationResult.Success);
-			operationB.Setup(o => o.Repeat()).Returns(OperationResult.Success);
+			operationB.Setup(o => o.Revert()).Returns(OperationResult.Success);
 			operationC.Setup(o => o.Perform()).Returns(OperationResult.Success);
-			operationC.Setup(o => o.Repeat()).Returns(OperationResult.Success);
+			operationC.Setup(o => o.Revert()).Returns(OperationResult.Success);
 
 			operations.Enqueue(operationA.Object);
 			operations.Enqueue(operationB.Object);
@@ -481,13 +328,13 @@ namespace SafeExamBrowser.Core.UnitTests.OperationModel
 
 			sut.TryPerform();
 
-			var success = sut.TryRevert();
+			var result = sut.TryRevert();
 
 			operationA.Verify(o => o.Revert(), Times.Once);
 			operationB.Verify(o => o.Revert(), Times.Once);
 			operationC.Verify(o => o.Revert(), Times.Once);
 
-			Assert.IsTrue(success);
+			Assert.AreEqual(OperationResult.Success, result);
 		}
 
 		[TestMethod]
@@ -515,9 +362,9 @@ namespace SafeExamBrowser.Core.UnitTests.OperationModel
 
 			sut.TryPerform();
 
-			var success = sut.TryRevert();
+			var result = sut.TryRevert();
 
-			Assert.IsTrue(success);
+			Assert.AreEqual(OperationResult.Success, result);
 			Assert.IsTrue(c == 1);
 			Assert.IsTrue(b == 2);
 			Assert.IsTrue(a == 3);
@@ -547,13 +394,13 @@ namespace SafeExamBrowser.Core.UnitTests.OperationModel
 
 			sut.TryPerform();
 
-			var success = sut.TryRevert();
+			var result = sut.TryRevert();
 
 			operationA.Verify(o => o.Revert(), Times.Once);
 			operationB.Verify(o => o.Revert(), Times.Once);
 			operationC.Verify(o => o.Revert(), Times.Once);
 
-			Assert.IsFalse(success);
+			Assert.AreEqual(OperationResult.Failed, result);
 		}
 
 		[TestMethod]
@@ -565,9 +412,9 @@ namespace SafeExamBrowser.Core.UnitTests.OperationModel
 			var operations = new Queue<IOperation>();
 
 			operationA.Setup(o => o.Perform()).Returns(OperationResult.Success);
-			operationA.Setup(o => o.Repeat()).Returns(OperationResult.Success);
+			operationA.Setup(o => o.Revert()).Returns(OperationResult.Success);
 			operationB.Setup(o => o.Perform()).Returns(OperationResult.Aborted);
-			operationB.Setup(o => o.Repeat()).Returns(OperationResult.Success);
+			operationB.Setup(o => o.Revert()).Returns(OperationResult.Success);
 
 			operations.Enqueue(operationA.Object);
 			operations.Enqueue(operationB.Object);
@@ -577,13 +424,13 @@ namespace SafeExamBrowser.Core.UnitTests.OperationModel
 
 			sut.TryPerform();
 
-			var success = sut.TryRevert();
+			var result = sut.TryRevert();
 
 			operationA.Verify(o => o.Revert(), Times.Once);
 			operationB.Verify(o => o.Revert(), Times.Once);
 			operationC.Verify(o => o.Revert(), Times.Never);
 
-			Assert.IsTrue(success);
+			Assert.AreEqual(OperationResult.Success, result);
 		}
 
 		[TestMethod]
@@ -592,16 +439,19 @@ namespace SafeExamBrowser.Core.UnitTests.OperationModel
 			var sut = new OperationSequence(loggerMock.Object, new Queue<IOperation>());
 
 			sut.TryPerform();
-			sut.TryRevert();
+
+			var result = sut.TryRevert();
+
+			Assert.AreEqual(OperationResult.Success, result);
 		}
 
 		[TestMethod]
 		public void MustSucceedRevertingWithoutCallingPerform()
 		{
 			var sut = new OperationSequence(loggerMock.Object, new Queue<IOperation>());
-			var success = sut.TryRevert();
+			var result = sut.TryRevert();
 
-			Assert.IsTrue(success);
+			Assert.AreEqual(OperationResult.Success, result);
 		}
 
 		[TestMethod]
@@ -611,9 +461,9 @@ namespace SafeExamBrowser.Core.UnitTests.OperationModel
 
 			sut.ProgressChanged += (args) => throw new Exception();
 
-			var success = sut.TryRevert();
+			var result = sut.TryRevert();
 
-			Assert.IsFalse(success);
+			Assert.AreEqual(OperationResult.Failed, result);
 		}
 
 		#endregion

SafeExamBrowser.Core.UnitTests/OperationModel/RepeatableOperationSequenceTests.cs

@@ -0,0 +1,177 @@
+/*
+ * Copyright (c) 2018 ETH Zürich, Educational Development and Technology (LET)
+ * 
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace SafeExamBrowser.Core.UnitTests.OperationModel
+{
+	[TestClass]
+	public class RepeatableOperationSequenceTests
+	{
+		[TestInitialize]
+		public void Initialize()
+		{
+
+		}
+
+		[TestMethod]
+		public void TODO()
+		{
+			Assert.Fail();
+		}
+
+		//[TestMethod]
+		//public void MustCorrectlyAbortRepeat()
+		//{
+		//	var operationA = new Mock<IOperation>();
+		//	var operationB = new Mock<IOperation>();
+		//	var operationC = new Mock<IOperation>();
+		//	var operations = new Queue<IOperation>();
+
+		//	operationA.Setup(o => o.Repeat()).Returns(OperationResult.Success);
+		//	operationB.Setup(o => o.Repeat()).Returns(OperationResult.Aborted);
+
+		//	operations.Enqueue(operationA.Object);
+		//	operations.Enqueue(operationB.Object);
+		//	operations.Enqueue(operationC.Object);
+
+		//	var sut = new OperationSequence(loggerMock.Object, operations);
+		//	var result = sut.TryRepeat();
+
+		//	operationA.Verify(o => o.Repeat(), Times.Once);
+		//	operationA.Verify(o => o.Revert(), Times.Never);
+		//	operationB.Verify(o => o.Repeat(), Times.Once);
+		//	operationB.Verify(o => o.Revert(), Times.Never);
+		//	operationC.Verify(o => o.Repeat(), Times.Never);
+		//	operationC.Verify(o => o.Revert(), Times.Never);
+
+		//	Assert.AreEqual(OperationResult.Aborted, result);
+		//}
+
+		//[TestMethod]
+		//public void MustRepeatOperations()
+		//{
+		//	var operationA = new Mock<IOperation>();
+		//	var operationB = new Mock<IOperation>();
+		//	var operationC = new Mock<IOperation>();
+		//	var operations = new Queue<IOperation>();
+
+		//	operationA.Setup(o => o.Repeat()).Returns(OperationResult.Success);
+		//	operationB.Setup(o => o.Repeat()).Returns(OperationResult.Success);
+		//	operationC.Setup(o => o.Repeat()).Returns(OperationResult.Success);
+
+		//	operations.Enqueue(operationA.Object);
+		//	operations.Enqueue(operationB.Object);
+		//	operations.Enqueue(operationC.Object);
+
+		//	var sut = new OperationSequence(loggerMock.Object, operations);
+		//	var result = sut.TryRepeat();
+
+		//	operationA.Verify(o => o.Perform(), Times.Never);
+		//	operationA.Verify(o => o.Repeat(), Times.Once);
+		//	operationA.Verify(o => o.Revert(), Times.Never);
+		//	operationB.Verify(o => o.Perform(), Times.Never);
+		//	operationB.Verify(o => o.Repeat(), Times.Once);
+		//	operationB.Verify(o => o.Revert(), Times.Never);
+		//	operationC.Verify(o => o.Perform(), Times.Never);
+		//	operationC.Verify(o => o.Repeat(), Times.Once);
+		//	operationC.Verify(o => o.Revert(), Times.Never);
+
+		//	Assert.AreEqual(OperationResult.Success, result);
+		//}
+
+		//[TestMethod]
+		//public void MustRepeatOperationsInSequence()
+		//{
+		//	int current = 0, a = 0, b = 0, c = 0;
+		//	var operationA = new Mock<IOperation>();
+		//	var operationB = new Mock<IOperation>();
+		//	var operationC = new Mock<IOperation>();
+		//	var operations = new Queue<IOperation>();
+
+		//	operationA.Setup(o => o.Repeat()).Returns(OperationResult.Success).Callback(() => a = ++current);
+		//	operationB.Setup(o => o.Repeat()).Returns(OperationResult.Success).Callback(() => b = ++current);
+		//	operationC.Setup(o => o.Repeat()).Returns(OperationResult.Success).Callback(() => c = ++current);
+
+		//	operations.Enqueue(operationA.Object);
+		//	operations.Enqueue(operationB.Object);
+		//	operations.Enqueue(operationC.Object);
+
+		//	var sut = new OperationSequence(loggerMock.Object, operations);
+		//	var result = sut.TryRepeat();
+
+		//	Assert.AreEqual(OperationResult.Success, result);
+		//	Assert.IsTrue(a == 1);
+		//	Assert.IsTrue(b == 2);
+		//	Assert.IsTrue(c == 3);
+		//}
+
+		//[TestMethod]
+		//public void MustNotRevertOperationsInCaseOfError()
+		//{
+		//	var operationA = new Mock<IOperation>();
+		//	var operationB = new Mock<IOperation>();
+		//	var operationC = new Mock<IOperation>();
+		//	var operationD = new Mock<IOperation>();
+		//	var operations = new Queue<IOperation>();
+
+		//	operationA.Setup(o => o.Repeat()).Returns(OperationResult.Success);
+		//	operationB.Setup(o => o.Repeat()).Returns(OperationResult.Success);
+		//	operationC.Setup(o => o.Repeat()).Throws<Exception>();
+
+		//	operations.Enqueue(operationA.Object);
+		//	operations.Enqueue(operationB.Object);
+		//	operations.Enqueue(operationC.Object);
+		//	operations.Enqueue(operationD.Object);
+
+		//	var sut = new OperationSequence(loggerMock.Object, operations);
+		//	var result = sut.TryRepeat();
+
+		//	operationA.Verify(o => o.Repeat(), Times.Once);
+		//	operationA.Verify(o => o.Revert(), Times.Never);
+		//	operationB.Verify(o => o.Repeat(), Times.Once);
+		//	operationB.Verify(o => o.Revert(), Times.Never);
+		//	operationC.Verify(o => o.Repeat(), Times.Once);
+		//	operationC.Verify(o => o.Revert(), Times.Never);
+		//	operationD.Verify(o => o.Repeat(), Times.Never);
+		//	operationD.Verify(o => o.Revert(), Times.Never);
+
+		//	Assert.AreEqual(OperationResult.Failed, result);
+		//}
+
+		//[TestMethod]
+		//public void MustSucceedRepeatingWithEmptyQueue()
+		//{
+		//	var sut = new OperationSequence(loggerMock.Object, new Queue<IOperation>());
+		//	var result = sut.TryRepeat();
+
+		//	Assert.AreEqual(OperationResult.Success, result);
+		//}
+
+		//[TestMethod]
+		//public void MustSucceedRepeatingWithoutCallingPerform()
+		//{
+		//	var sut = new OperationSequence(loggerMock.Object, new Queue<IOperation>());
+		//	var result = sut.TryRepeat();
+
+		//	Assert.AreEqual(OperationResult.Success, result);
+		//}
+
+		//[TestMethod]
+		//public void MustNotFailInCaseOfUnexpectedErrorWhenRepeating()
+		//{
+		//	var sut = new OperationSequence(loggerMock.Object, new Queue<IOperation>());
+
+		//	sut.ProgressChanged += (args) => throw new Exception();
+
+		//	var result = sut.TryRepeat();
+
+		//	Assert.AreEqual(OperationResult.Failed, result);
+		//}
+	}
+}

SafeExamBrowser.Core.UnitTests/Operations/DelegateOperationTests.cs

@@ -58,11 +58,11 @@ namespace SafeExamBrowser.Core.UnitTests.Operations
 
 			var perform = sut.Perform();
 			var repeat = sut.Repeat();
-
+			var revert = sut.Revert();
-			sut.Revert();
 
 			Assert.AreEqual(OperationResult.Success, perform);
 			Assert.AreEqual(OperationResult.Success, repeat);
+			Assert.AreEqual(OperationResult.Success, revert);
 		}
 	}
 }

SafeExamBrowser.Core.UnitTests/Operations/I18nOperationTests.cs

@@ -6,7 +6,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-using System;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Moq;
 using SafeExamBrowser.Contracts.Core.OperationModel;
@@ -52,12 +51,5 @@ namespace SafeExamBrowser.Core.UnitTests.Operations
 
 			text.VerifyNoOtherCalls();
 		}
-
-		[TestMethod]
-		[ExpectedException(typeof(InvalidOperationException))]
-		public void MustNotAllowRepeating()
-		{
-			sut.Repeat();
-		}
 	}
 }

SafeExamBrowser.Core.UnitTests/Operations/LazyInitializationOperationTests.cs

@@ -45,20 +45,6 @@ namespace SafeExamBrowser.Core.UnitTests.Operations
 			Assert.IsTrue(initialized);
 		}
 
-		[TestMethod]
-		[ExpectedException(typeof(NullReferenceException))]
-		public void MustNotInstantiateOperationOnRepeat()
-		{
-			IOperation initialize()
-			{
-				return operationMock.Object;
-			};
-
-			var sut = new LazyInitializationOperation(initialize);
-
-			sut.Repeat();
-		}
-
 		[TestMethod]
 		[ExpectedException(typeof(NullReferenceException))]
 		public void MustNotInstantiateOperationOnRevert()
@@ -82,16 +68,14 @@ namespace SafeExamBrowser.Core.UnitTests.Operations
 			};
 
 			operationMock.Setup(o => o.Perform()).Returns(OperationResult.Success);
-			operationMock.Setup(o => o.Repeat()).Returns(OperationResult.Failed);
+			operationMock.Setup(o => o.Revert()).Returns(OperationResult.Failed);
 
 			var sut = new LazyInitializationOperation(initialize);
 			var perform = sut.Perform();
-			var repeat = sut.Repeat();
+			var revert = sut.Revert();
-
-			sut.Revert();
 
 			Assert.AreEqual(OperationResult.Success, perform);
-			Assert.AreEqual(OperationResult.Failed, repeat);
+			Assert.AreEqual(OperationResult.Failed, revert);
 		}
 
 		[TestMethod]
@@ -147,6 +131,8 @@ namespace SafeExamBrowser.Core.UnitTests.Operations
 			{
 				if (first)
 				{
+					first = false;
+
 					return operation;
 				}
 
@@ -156,11 +142,9 @@ namespace SafeExamBrowser.Core.UnitTests.Operations
 			var sut = new LazyInitializationOperation(initialize);
 
 			sut.Perform();
-			sut.Repeat();
 			sut.Revert();
 
 			operationMock.Verify(o => o.Perform(), Times.Once);
-			operationMock.Verify(o => o.Repeat(), Times.Once);
 			operationMock.Verify(o => o.Revert(), Times.Once);
 		}
 	}

SafeExamBrowser.Core.UnitTests/SafeExamBrowser.Core.UnitTests.csproj

@@ -79,6 +79,7 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="OperationModel\QueueExtensionTests.cs" />
+    <Compile Include="OperationModel\RepeatableOperationSequenceTests.cs" />
     <Compile Include="Operations\CommunicationHostOperationTests.cs" />
     <Compile Include="Operations\LazyInitializationOperationTests.cs" />
     <Compile Include="Operations\I18nOperationTests.cs" />

SafeExamBrowser.Core/OperationModel/OperationSequence.cs

@@ -20,9 +20,9 @@ namespace SafeExamBrowser.Core.OperationModel
 	/// </summary>
 	public class OperationSequence : IOperationSequence
 	{
-		private ILogger logger;
+		protected ILogger logger;
-		private Queue<IOperation> operations = new Queue<IOperation>();
+		protected Queue<IOperation> operations = new Queue<IOperation>();
-		private Stack<IOperation> stack = new Stack<IOperation>();
+		protected Stack<IOperation> stack = new Stack<IOperation>();
 
 		public event ActionRequiredEventHandler ActionRequired
 		{
@@ -44,7 +44,7 @@ namespace SafeExamBrowser.Core.OperationModel
 			this.operations = new Queue<IOperation>(operations);
 		}
 
-		public OperationResult TryPerform()
+		public virtual OperationResult TryPerform()
 		{
 			var result = OperationResult.Failed;
 
@@ -66,53 +66,36 @@ namespace SafeExamBrowser.Core.OperationModel
 			return result;
 		}
 
-		public OperationResult TryRepeat()
+		public virtual OperationResult TryRevert()
 		{
 			var result = OperationResult.Failed;
 
-			try
-			{
-				Initialize();
-				result = Repeat();
-			}
-			catch (Exception e)
-			{
-				logger.Error("Failed to repeat operations!", e);
-			}
-
-			return result;
-		}
-
-		public bool TryRevert()
-		{
-			var success = false;
-
 			try
 			{
 				Initialize(true);
-				success = Revert();
+				result = Revert();
 			}
 			catch (Exception e)
 			{
 				logger.Error("Failed to revert operations!", e);
 			}
 
-			return success;
+			return result;
 		}
 
-		private void Initialize(bool indeterminate = false)
+		protected virtual void Initialize(bool indeterminate = false)
 		{
 			if (indeterminate)
 			{
-				ProgressChanged?.Invoke(new ProgressChangedEventArgs { IsIndeterminate = true });
+				UpdateProgress(new ProgressChangedEventArgs { IsIndeterminate = true });
 			}
 			else
 			{
-				ProgressChanged?.Invoke(new ProgressChangedEventArgs { CurrentValue = 0, MaxValue = operations.Count });
+				UpdateProgress(new ProgressChangedEventArgs { CurrentValue = 0, MaxValue = operations.Count });
 			}
 		}
 
-		private OperationResult Perform()
+		protected virtual OperationResult Perform()
 		{
 			foreach (var operation in operations)
 			{
@@ -134,39 +117,13 @@ namespace SafeExamBrowser.Core.OperationModel
 					return result;
 				}
 
-				ProgressChanged?.Invoke(new ProgressChangedEventArgs { Progress = true });
+				UpdateProgress(new ProgressChangedEventArgs { Progress = true });
 			}
 
 			return OperationResult.Success;
 		}
 
-		private OperationResult Repeat()
+		protected virtual OperationResult Revert(bool regress = false)
-		{
-			foreach (var operation in operations)
-			{
-				var result = OperationResult.Failed;
-
-				try
-				{
-					result = operation.Repeat();
-				}
-				catch (Exception e)
-				{
-					logger.Error($"Caught unexpected exception while repeating operation '{operation.GetType().Name}'!", e);
-				}
-
-				if (result != OperationResult.Success)
-				{
-					return result;
-				}
-
-				ProgressChanged?.Invoke(new ProgressChangedEventArgs { Progress = true });
-			}
-
-			return OperationResult.Success;
-		}
-
-		private bool Revert(bool regress = false)
 		{
 			var success = true;
 
@@ -176,21 +133,31 @@ namespace SafeExamBrowser.Core.OperationModel
 
 				try
 				{
-					operation.Revert();
+					var result = operation.Revert();
+
+					if (result != OperationResult.Success)
+					{
+						success = false;
+					}
 				}
 				catch (Exception e)
 				{
-					logger.Error($"Failed to revert operation '{operation.GetType().Name}'!", e);
+					logger.Error($"Caught unexpected exception while reverting operation '{operation.GetType().Name}'!", e);
 					success = false;
 				}
 
 				if (regress)
 				{
-					ProgressChanged?.Invoke(new ProgressChangedEventArgs { Regress = true });
+					UpdateProgress(new ProgressChangedEventArgs { Regress = true });
 				}
 			}
 
-			return success;
+			return success ? OperationResult.Success : OperationResult.Failed;
+		}
+
+		protected void UpdateProgress(ProgressChangedEventArgs args)
+		{
+			ProgressChanged?.Invoke(args);
 		}
 	}
 }

SafeExamBrowser.Core/OperationModel/RepeatableOperationSequence.cs

@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2018 ETH Zürich, Educational Development and Technology (LET)
+ * 
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+using System;
+using System.Collections.Generic;
+using SafeExamBrowser.Contracts.Core.OperationModel;
+using SafeExamBrowser.Contracts.Core.OperationModel.Events;
+using SafeExamBrowser.Contracts.Logging;
+
+namespace SafeExamBrowser.Core.OperationModel
+{
+	/// <summary>
+	/// Default implementation of the <see cref="IRepeatableOperationSequence"/>.
+	/// </summary>
+	public class RepeatableOperationSequence : OperationSequence, IRepeatableOperationSequence
+	{
+		private new Queue<IRepeatableOperation> operations;
+
+		public RepeatableOperationSequence(ILogger logger, Queue<IRepeatableOperation> operations) : base(logger, new Queue<IOperation>(operations))
+		{
+			this.operations = new Queue<IRepeatableOperation>(operations);
+		}
+
+		public OperationResult TryRepeat()
+		{
+			var result = OperationResult.Failed;
+
+			try
+			{
+				Initialize();
+				result = Repeat();
+			}
+			catch (Exception e)
+			{
+				logger.Error("Failed to repeat operations!", e);
+			}
+
+			return result;
+		}
+
+		private OperationResult Repeat()
+		{
+			foreach (var operation in operations)
+			{
+				var result = OperationResult.Failed;
+
+				try
+				{
+					result = operation.Repeat();
+				}
+				catch (Exception e)
+				{
+					logger.Error($"Caught unexpected exception while repeating operation '{operation.GetType().Name}'!", e);
+				}
+
+				if (result != OperationResult.Success)
+				{
+					return result;
+				}
+
+				UpdateProgress(new ProgressChangedEventArgs { Progress = true });
+			}
+
+			return OperationResult.Success;
+		}
+	}
+}

SafeExamBrowser.Core/Operations/CommunicationHostOperation.cs

@@ -18,7 +18,7 @@ namespace SafeExamBrowser.Core.Operations
 	/// An operation to handle the lifetime of an <see cref="ICommunicationHost"/>. The host is started during <see cref="Perform"/>,
 	/// stopped and restarted during <see cref="Repeat"/> (if not running) and stopped during <see cref="Revert"/>.
 	/// </summary>
-	public class CommunicationHostOperation : IOperation
+	public class CommunicationHostOperation : IRepeatableOperation
 	{
 		private ICommunicationHost host;
 		private ILogger logger;
@@ -56,12 +56,14 @@ namespace SafeExamBrowser.Core.Operations
 			return OperationResult.Success;
 		}
 
-		public void Revert()
+		public OperationResult Revert()
 		{
 			logger.Info("Stopping communication host...");
 			StatusChanged?.Invoke(TextKey.OperationStatus_StopCommunicationHost);
 
 			host.Stop();
+
+			return OperationResult.Success;
 		}
 	}
 }

SafeExamBrowser.Core/Operations/DelegateOperation.cs

@@ -16,7 +16,7 @@ namespace SafeExamBrowser.Core.Operations
 	/// A generic operation to allow for the (inline) definition of an operation via delegates. Useful if implementing a complete
 	/// <see cref="IOperation"/> would be an unnecessary overhead.
 	/// </summary>
-	public class DelegateOperation : IOperation
+	public class DelegateOperation : IRepeatableOperation
 	{
 		private Action perform;
 		private Action repeat;
@@ -46,9 +46,11 @@ namespace SafeExamBrowser.Core.Operations
 			return OperationResult.Success;
 		}
 
-		public void Revert()
+		public OperationResult Revert()
 		{
 			revert?.Invoke();
+
+			return OperationResult.Success;
 		}
 	}
 }

SafeExamBrowser.Core/Operations/I18nOperation.cs

@@ -6,7 +6,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-using System;
 using System.Globalization;
 using SafeExamBrowser.Contracts.Core.OperationModel;
 using SafeExamBrowser.Contracts.Core.OperationModel.Events;
@@ -43,14 +42,9 @@ namespace SafeExamBrowser.Core.Operations
 			return OperationResult.Success;
 		}
 
-		public OperationResult Repeat()
+		public OperationResult Revert()
 		{
-			throw new InvalidOperationException($"The '{nameof(I18nOperation)}' is not meant to be repeated!");
+			return OperationResult.Success;
-		}
-
-		public void Revert()
-		{
-			// Nothing to do here...
 		}
 	}
 }

SafeExamBrowser.Core/Operations/LazyInitializationOperation.cs

@@ -83,14 +83,9 @@ namespace SafeExamBrowser.Core.Operations
 			return operation.Perform();
 		}
 
-		public OperationResult Repeat()
+		public OperationResult Revert()
 		{
-			return operation.Repeat();
+			return operation.Revert();
-		}
-
-		public void Revert()
-		{
-			operation.Revert();
 		}
 	}
 }

SafeExamBrowser.Core/SafeExamBrowser.Core.csproj

@@ -55,6 +55,7 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="OperationModel\QueueExtensions.cs" />
+    <Compile Include="OperationModel\RepeatableOperationSequence.cs" />
     <Compile Include="Operations\CommunicationHostOperation.cs" />
     <Compile Include="Operations\LazyInitializationOperation.cs" />
     <Compile Include="Operations\I18nOperation.cs" />

SafeExamBrowser.Monitoring/Windows/WindowMonitor.cs

@@ -117,7 +117,7 @@ namespace SafeExamBrowser.Monitoring.Windows
 
 		private void OnWindowChanged(IntPtr window)
 		{
-			if (activeWindow != window)
+			if (window != IntPtr.Zero && activeWindow != window)
 			{
 				logger.Debug($"Window has changed from {activeWindow} to {window}.");
 				activeWindow = window;

SafeExamBrowser.Runtime.UnitTests/Operations/ClientOperationTests.cs

@@ -84,26 +84,6 @@ namespace SafeExamBrowser.Runtime.UnitTests.Operations
 			Assert.AreEqual(OperationResult.Success, result);
 		}
 
-		[TestMethod]
-		public void MustStartClientWhenRepeating()
-		{
-			var result = default(OperationResult);
-			var response = new AuthenticationResponse { ProcessId = 1234 };
-			var communication = new CommunicationResult<AuthenticationResponse>(true, response);
-
-			process.SetupGet(p => p.Id).Returns(response.ProcessId);
-			processFactory.Setup(f => f.StartNew(It.IsAny<string>(), It.IsAny<string[]>())).Returns(process.Object).Callback(clientReady);
-			proxy.Setup(p => p.RequestAuthentication()).Returns(communication);
-			proxy.Setup(p => p.Connect(It.IsAny<Guid>(), true)).Returns(true);
-
-			result = sut.Repeat();
-
-			session.VerifySet(s => s.ClientProcess = process.Object, Times.Once);
-			session.VerifySet(s => s.ClientProxy = proxy.Object, Times.Once);
-
-			Assert.AreEqual(OperationResult.Success, result);
-		}
-
 		[TestMethod]
 		public void MustFailStartupIfClientNotStartedWithinTimeout()
 		{
@@ -153,6 +133,87 @@ namespace SafeExamBrowser.Runtime.UnitTests.Operations
 			Assert.AreEqual(OperationResult.Failed, result);
 		}
 
+		[TestMethod]
+		public void MustStartClientWhenRepeating()
+		{
+			var result = default(OperationResult);
+			var response = new AuthenticationResponse { ProcessId = 1234 };
+			var communication = new CommunicationResult<AuthenticationResponse>(true, response);
+
+			process.SetupGet(p => p.Id).Returns(response.ProcessId);
+			processFactory.Setup(f => f.StartNew(It.IsAny<string>(), It.IsAny<string[]>())).Returns(process.Object).Callback(clientReady);
+			proxy.Setup(p => p.RequestAuthentication()).Returns(communication);
+			proxy.Setup(p => p.Connect(It.IsAny<Guid>(), true)).Returns(true);
+
+			result = sut.Repeat();
+
+			session.VerifySet(s => s.ClientProcess = process.Object, Times.Once);
+			session.VerifySet(s => s.ClientProxy = proxy.Object, Times.Once);
+
+			Assert.AreEqual(OperationResult.Success, result);
+		}
+
+		[TestMethod]
+		public void MustTerminateClientOnRepeat()
+		{
+			var terminated = new Action(() =>
+			{
+				runtimeHost.Raise(h => h.ClientDisconnected += null);
+				process.Raise(p => p.Terminated += null, 0);
+			});
+
+			proxy.Setup(p => p.Disconnect()).Callback(terminated);
+			session.SetupGet(s => s.ClientProcess).Returns(process.Object);
+
+			var result = sut.Repeat();
+
+			proxy.Verify(p => p.InitiateShutdown(), Times.Once);
+			proxy.Verify(p => p.Disconnect(), Times.Once);
+			process.Verify(p => p.Kill(), Times.Never);
+			session.VerifySet(s => s.ClientProcess = null, Times.Once);
+			session.VerifySet(s => s.ClientProxy = null, Times.Once);
+
+			Assert.AreEqual(OperationResult.Success, result);
+		}
+
+		[TestMethod]
+		public void MustDoNothingIfNoClientCreated()
+		{
+			session.SetupGet(s => s.ClientProcess).Returns(null as IProcess);
+
+			var result = sut.Repeat();
+
+			session.VerifyGet(s => s.ClientProcess, Times.Once);
+
+			process.VerifyNoOtherCalls();
+			processFactory.VerifyNoOtherCalls();
+			proxy.VerifyNoOtherCalls();
+			proxyFactory.VerifyNoOtherCalls();
+			runtimeHost.VerifyNoOtherCalls();
+
+			Assert.AreEqual(OperationResult.Success, result);
+		}
+
+		[TestMethod]
+		public void MustDoNothingIfNoClientRunning()
+		{
+			process.SetupGet(p => p.HasTerminated).Returns(true);
+			session.SetupGet(s => s.ClientProcess).Returns(process.Object);
+
+			var result = sut.Repeat();
+
+			process.VerifyGet(p => p.HasTerminated, Times.Once);
+			session.VerifyGet(s => s.ClientProcess, Times.Exactly(2));
+
+			process.VerifyNoOtherCalls();
+			processFactory.VerifyNoOtherCalls();
+			proxy.VerifyNoOtherCalls();
+			proxyFactory.VerifyNoOtherCalls();
+			runtimeHost.VerifyNoOtherCalls();
+
+			Assert.AreEqual(OperationResult.Success, result);
+		}
+
 		[TestMethod]
 		public void MustStopClientWhenReverting()
 		{

SafeExamBrowser.Runtime.UnitTests/Operations/ClientTerminationOperationTests.cs

@@ -1,144 +0,0 @@
-/*
- * Copyright (c) 2018 ETH Zürich, Educational Development and Technology (LET)
- * 
- * This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/.
- */
-
-using System;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
-using Moq;
-using SafeExamBrowser.Contracts.Communication.Hosts;
-using SafeExamBrowser.Contracts.Communication.Proxies;
-using SafeExamBrowser.Contracts.Configuration;
-using SafeExamBrowser.Contracts.Core.OperationModel;
-using SafeExamBrowser.Contracts.Logging;
-using SafeExamBrowser.Contracts.WindowsApi;
-using SafeExamBrowser.Runtime.Operations;
-
-namespace SafeExamBrowser.Runtime.UnitTests.Operations
-{
-	[TestClass]
-	public class ClientTerminationOperationTests
-	{
-		private Action clientReady;
-		private AppConfig appConfig;
-		private Mock<IConfigurationRepository> configuration;
-		private Mock<IClientProxy> proxy;
-		private Mock<ILogger> logger;
-		private Mock<IProcess> process;
-		private Mock<IProcessFactory> processFactory;
-		private Mock<IProxyFactory> proxyFactory;
-		private Mock<IRuntimeHost> runtimeHost;
-		private Mock<ISessionData> session;
-		private ClientTerminationOperation sut;
-
-		[TestInitialize]
-		public void Initialize()
-		{
-			appConfig = new AppConfig();
-			configuration = new Mock<IConfigurationRepository>();
-			clientReady = new Action(() => runtimeHost.Raise(h => h.ClientReady += null));
-			logger = new Mock<ILogger>();
-			process = new Mock<IProcess>();
-			processFactory = new Mock<IProcessFactory>();
-			proxy = new Mock<IClientProxy>();
-			proxyFactory = new Mock<IProxyFactory>();
-			runtimeHost = new Mock<IRuntimeHost>();
-			session = new Mock<ISessionData>();
-
-			configuration.SetupGet(c => c.CurrentSession).Returns(session.Object);
-			configuration.SetupGet(c => c.AppConfig).Returns(appConfig);
-			proxyFactory.Setup(f => f.CreateClientProxy(It.IsAny<string>())).Returns(proxy.Object);
-			session.SetupGet(s => s.ClientProxy).Returns(proxy.Object);
-
-			sut = new ClientTerminationOperation(configuration.Object, logger.Object, processFactory.Object, proxyFactory.Object, runtimeHost.Object, 0);
-		}
-
-		[TestMethod]
-		public void MustDoNothingOnPerform()
-		{
-			sut.Perform();
-
-			process.VerifyNoOtherCalls();
-			processFactory.VerifyNoOtherCalls();
-			proxy.VerifyNoOtherCalls();
-			proxyFactory.VerifyNoOtherCalls();
-			runtimeHost.VerifyNoOtherCalls();
-		}
-
-		[TestMethod]
-		public void MustDoNothingOnRevert()
-		{
-			sut.Revert();
-
-			process.VerifyNoOtherCalls();
-			processFactory.VerifyNoOtherCalls();
-			proxy.VerifyNoOtherCalls();
-			proxyFactory.VerifyNoOtherCalls();
-			runtimeHost.VerifyNoOtherCalls();
-		}
-
-		[TestMethod]
-		public void MustTerminateClientOnRepeat()
-		{
-			var terminated = new Action(() =>
-			{
-				runtimeHost.Raise(h => h.ClientDisconnected += null);
-				process.Raise(p => p.Terminated += null, 0);
-			});
-
-			proxy.Setup(p => p.Disconnect()).Callback(terminated);
-			session.SetupGet(s => s.ClientProcess).Returns(process.Object);
-
-			var result = sut.Repeat();
-
-			proxy.Verify(p => p.InitiateShutdown(), Times.Once);
-			proxy.Verify(p => p.Disconnect(), Times.Once);
-			process.Verify(p => p.Kill(), Times.Never);
-			session.VerifySet(s => s.ClientProcess = null, Times.Once);
-			session.VerifySet(s => s.ClientProxy = null, Times.Once);
-
-			Assert.AreEqual(OperationResult.Success, result);
-		}
-
-		[TestMethod]
-		public void MustDoNothingIfNoClientCreated()
-		{
-			session.SetupGet(s => s.ClientProcess).Returns(null as IProcess);
-
-			var result = sut.Repeat();
-
-			session.VerifyGet(s => s.ClientProcess, Times.Once);
-
-			process.VerifyNoOtherCalls();
-			processFactory.VerifyNoOtherCalls();
-			proxy.VerifyNoOtherCalls();
-			proxyFactory.VerifyNoOtherCalls();
-			runtimeHost.VerifyNoOtherCalls();
-
-			Assert.AreEqual(OperationResult.Success, result);
-		}
-
-		[TestMethod]
-		public void MustDoNothingIfNoClientRunning()
-		{
-			process.SetupGet(p => p.HasTerminated).Returns(true);
-			session.SetupGet(s => s.ClientProcess).Returns(process.Object);
-
-			var result = sut.Repeat();
-
-			process.VerifyGet(p => p.HasTerminated, Times.Once);
-			session.VerifyGet(s => s.ClientProcess, Times.Exactly(2));
-
-			process.VerifyNoOtherCalls();
-			processFactory.VerifyNoOtherCalls();
-			proxy.VerifyNoOtherCalls();
-			proxyFactory.VerifyNoOtherCalls();
-			runtimeHost.VerifyNoOtherCalls();
-
-			Assert.AreEqual(OperationResult.Success, result);
-		}
-	}
-}

SafeExamBrowser.Runtime.UnitTests/Operations/KioskModeOperationTests.cs

@@ -90,8 +90,8 @@ namespace SafeExamBrowser.Runtime.UnitTests.Operations
 		[TestMethod]
 		public void MustCorrectlyRevertCreateNewDesktop()
 		{
-			var originalDesktop = new Mock<IDesktop>();
 			var newDesktop = new Mock<IDesktop>();
+			var originalDesktop = new Mock<IDesktop>();
 			var order = 0;
 			var activate = 0;
 			var setStartup = 0;
@@ -135,8 +135,8 @@ namespace SafeExamBrowser.Runtime.UnitTests.Operations
 		[TestMethod]
 		public void MustCorrectlySwitchToOtherKioskModeWhenRepeating()
 		{
-			var originalDesktop = new Mock<IDesktop>();
 			var newDesktop = new Mock<IDesktop>();
+			var originalDesktop = new Mock<IDesktop>();
 
 			desktopFactory.Setup(f => f.GetCurrent()).Returns(originalDesktop.Object);
 			desktopFactory.Setup(f => f.CreateNew(It.IsAny<string>())).Returns(newDesktop.Object);
@@ -192,8 +192,8 @@ namespace SafeExamBrowser.Runtime.UnitTests.Operations
 		[TestMethod]
 		public void MustNotReinitializeCreateNewDesktopWhenRepeating()
 		{
-			var originalDesktop = new Mock<IDesktop>();
 			var newDesktop = new Mock<IDesktop>();
+			var originalDesktop = new Mock<IDesktop>();
 
 			settings.KioskMode = KioskMode.CreateNewDesktop;
 

SafeExamBrowser.Runtime.UnitTests/SafeExamBrowser.Runtime.UnitTests.csproj

@@ -83,7 +83,6 @@
     <Compile Include="Operations\KioskModeOperationTests.cs" />
     <Compile Include="Operations\ServiceOperationTests.cs" />
     <Compile Include="Operations\ClientOperationTests.cs" />
-    <Compile Include="Operations\ClientTerminationOperationTests.cs" />
     <Compile Include="Operations\SessionInitializationOperationTests.cs" />
     <Compile Include="RuntimeControllerTests.cs" />
     <Compile Include="Communication\RuntimeHostTests.cs" />

SafeExamBrowser.Runtime/CompositionRoot.cs

@@ -66,20 +66,21 @@ namespace SafeExamBrowser.Runtime
 			var uiFactory = new UserInterfaceFactory(text);
 
 			var bootstrapOperations = new Queue<IOperation>();
-			var sessionOperations = new Queue<IOperation>();
+			var sessionOperations = new Queue<IRepeatableOperation>();
 
 			bootstrapOperations.Enqueue(new I18nOperation(logger, text, textResource));
 			bootstrapOperations.Enqueue(new CommunicationHostOperation(runtimeHost, logger));
 
 			sessionOperations.Enqueue(new ConfigurationOperation(appConfig, configuration, logger, resourceLoader, args));
+			sessionOperations.Enqueue(new ClientTerminationOperation(configuration, logger, processFactory, proxyFactory, runtimeHost, FIFTEEN_SECONDS));
+			sessionOperations.Enqueue(new KioskModeTerminationOperation(configuration, desktopFactory, explorerShell, logger, processFactory));
 			sessionOperations.Enqueue(new SessionInitializationOperation(configuration, logger, runtimeHost));
 			sessionOperations.Enqueue(new ServiceOperation(configuration, logger, serviceProxy));
-			sessionOperations.Enqueue(new ClientTerminationOperation(configuration, logger, processFactory, proxyFactory, runtimeHost, FIFTEEN_SECONDS));
 			sessionOperations.Enqueue(new KioskModeOperation(configuration, desktopFactory, explorerShell, logger, processFactory));
 			sessionOperations.Enqueue(new ClientOperation(configuration, logger, processFactory, proxyFactory, runtimeHost, FIFTEEN_SECONDS));
 
 			var bootstrapSequence = new OperationSequence(logger, bootstrapOperations);
-			var sessionSequence = new OperationSequence(logger, sessionOperations);
+			var sessionSequence = new RepeatableOperationSequence(logger, sessionOperations);
 
 			RuntimeController = new RuntimeController(appConfig, configuration, logger, messageBox, bootstrapSequence, sessionSequence, runtimeHost, serviceProxy, shutdown, text, uiFactory);
 		}

SafeExamBrowser.Runtime/Operations/ClientOperation.cs

@@ -20,26 +20,26 @@ using SafeExamBrowser.Contracts.WindowsApi.Events;
 
 namespace SafeExamBrowser.Runtime.Operations
 {
-	internal class ClientOperation : IOperation
+	internal class ClientOperation : IRepeatableOperation
 	{
 		private readonly int timeout_ms;
 
-		protected IConfigurationRepository configuration;
+		private IConfigurationRepository configuration;
-		protected ILogger logger;
+		private ILogger logger;
-		protected IProcessFactory processFactory;
+		private IProcessFactory processFactory;
-		protected IProxyFactory proxyFactory;
+		private IProxyFactory proxyFactory;
-		protected IRuntimeHost runtimeHost;
+		private IRuntimeHost runtimeHost;
 
 		public event ActionRequiredEventHandler ActionRequired { add { } remove { } }
 		public event StatusChangedEventHandler StatusChanged;
 
-		protected IProcess ClientProcess
+		private IProcess ClientProcess
 		{
 			get { return configuration.CurrentSession.ClientProcess; }
 			set { configuration.CurrentSession.ClientProcess = value; }
 		}
 
-		protected IClientProxy ClientProxy
+		private IClientProxy ClientProxy
 		{
 			get { return configuration.CurrentSession.ClientProxy; }
 			set { configuration.CurrentSession.ClientProxy = value; }
@@ -84,16 +84,20 @@ namespace SafeExamBrowser.Runtime.Operations
 			return Perform();
 		}
 
-		public virtual void Revert()
+		public virtual OperationResult Revert()
 		{
+			var success = true;
+
 			if (ClientProcess != null && !ClientProcess.HasTerminated)
 			{
 				StatusChanged?.Invoke(TextKey.OperationStatus_StopClient);
-				TryStopClient();
+				success = TryStopClient();
-			}
 			}
 
-		protected bool TryStartClient()
+			return success ? OperationResult.Success : OperationResult.Failed;
+		}
+
+		private bool TryStartClient()
 		{
 			var clientReady = false;
 			var clientReadyEvent = new AutoResetEvent(false);
@@ -146,7 +150,7 @@ namespace SafeExamBrowser.Runtime.Operations
 			return true;
 		}
 
-		protected bool TryStopClient()
+		private bool TryStopClient()
 		{
 			var success = false;
 
@@ -206,7 +210,7 @@ namespace SafeExamBrowser.Runtime.Operations
 			return success;
 		}
 
-		protected bool TryKillClient(int attempt = 0)
+		private bool TryKillClient(int attempt = 0)
 		{
 			const int MAX_ATTEMPTS = 5;
 

SafeExamBrowser.Runtime/Operations/ClientTerminationOperation.cs

@@ -10,18 +10,13 @@ using SafeExamBrowser.Contracts.Communication.Hosts;
 using SafeExamBrowser.Contracts.Communication.Proxies;
 using SafeExamBrowser.Contracts.Configuration;
 using SafeExamBrowser.Contracts.Core.OperationModel;
-using SafeExamBrowser.Contracts.Core.OperationModel.Events;
-using SafeExamBrowser.Contracts.I18n;
 using SafeExamBrowser.Contracts.Logging;
 using SafeExamBrowser.Contracts.WindowsApi;
 
 namespace SafeExamBrowser.Runtime.Operations
 {
-	internal class ClientTerminationOperation : ClientOperation
+	internal class ClientTerminationOperation : ClientOperation, IRepeatableOperation
 	{
-		public new event ActionRequiredEventHandler ActionRequired { add { } remove { } }
-		public new event StatusChangedEventHandler StatusChanged;
-
 		public ClientTerminationOperation(
 			IConfigurationRepository configuration,
 			ILogger logger,
@@ -39,20 +34,12 @@ namespace SafeExamBrowser.Runtime.Operations
 
 		public override OperationResult Repeat()
 		{
-			var success = true;
+			return base.Revert();
+		}
 
-			if (ClientProcess != null && !ClientProcess.HasTerminated)
+		public override OperationResult Revert()
 		{
-				StatusChanged?.Invoke(TextKey.OperationStatus_StopClient);
+			return OperationResult.Success;
-				success = TryStopClient();
-			}
-
-			return success ? OperationResult.Success : OperationResult.Failed;
-		}
-
-		public override void Revert()
-		{
-			// Nothing to do here...
 		}
 	}
 }

SafeExamBrowser.Runtime/Operations/ConfigurationOperation.cs

@@ -19,7 +19,7 @@ using SafeExamBrowser.Runtime.Operations.Events;
 
 namespace SafeExamBrowser.Runtime.Operations
 {
-	internal class ConfigurationOperation : IOperation
+	internal class ConfigurationOperation : IRepeatableOperation
 	{
 		private IConfigurationRepository configuration;
 		private ILogger logger;
@@ -92,9 +92,9 @@ namespace SafeExamBrowser.Runtime.Operations
 			return OperationResult.Failed;
 		}
 
-		public void Revert()
+		public OperationResult Revert()
 		{
-			// Nothing to do here...
+			return OperationResult.Success;
 		}
 
 		private OperationResult LoadSettings(Uri uri)

SafeExamBrowser.Runtime/Operations/KioskModeOperation.cs

@@ -16,7 +16,7 @@ using SafeExamBrowser.Contracts.WindowsApi;
 
 namespace SafeExamBrowser.Runtime.Operations
 {
-	internal class KioskModeOperation : IOperation
+	internal class KioskModeOperation : IRepeatableOperation
 	{
 		private IConfigurationRepository configuration;
 		private IDesktopFactory desktopFactory;
@@ -24,12 +24,22 @@ namespace SafeExamBrowser.Runtime.Operations
 		private KioskMode kioskMode;
 		private ILogger logger;
 		private IProcessFactory processFactory;
-		private IDesktop newDesktop;
-		private IDesktop originalDesktop;
 
 		public event ActionRequiredEventHandler ActionRequired { add { } remove { } }
 		public event StatusChangedEventHandler StatusChanged;
 
+		private IDesktop NewDesktop
+		{
+			get { return configuration.CurrentSession.NewDesktop; }
+			set { configuration.CurrentSession.NewDesktop = value; }
+		}
+
+		private IDesktop OriginalDesktop
+		{
+			get { return configuration.CurrentSession.OriginalDesktop; }
+			set { configuration.CurrentSession.OriginalDesktop = value; }
+		}
+
 		public KioskModeOperation(
 			IConfigurationRepository configuration,
 			IDesktopFactory desktopFactory,
@@ -44,7 +54,7 @@ namespace SafeExamBrowser.Runtime.Operations
 			this.processFactory = processFactory;
 		}
 
-		public OperationResult Perform()
+		public virtual OperationResult Perform()
 		{
 			kioskMode = configuration.CurrentSettings.KioskMode;
 
@@ -64,7 +74,7 @@ namespace SafeExamBrowser.Runtime.Operations
 			return OperationResult.Success;
 		}
 
-		public OperationResult Repeat()
+		public virtual OperationResult Repeat()
 		{
 			var oldMode = kioskMode;
 			var newMode = configuration.CurrentSettings.KioskMode;
@@ -72,19 +82,14 @@ namespace SafeExamBrowser.Runtime.Operations
 			if (newMode == oldMode)
 			{
 				logger.Info($"New kiosk mode '{newMode}' is equal to the currently active '{oldMode}', skipping re-initialization...");
-			}
-			else
-			{
-				Revert();
-				Perform();
-			}
-
-			kioskMode = newMode;
 
 				return OperationResult.Success;
 			}
 
-		public void Revert()
+			return Perform();
+		}
+
+		public virtual OperationResult Revert()
 		{
 			logger.Info($"Reverting kiosk mode '{kioskMode}'...");
 			StatusChanged?.Invoke(TextKey.OperationStatus_RevertKioskMode);
@@ -98,18 +103,20 @@ namespace SafeExamBrowser.Runtime.Operations
 					RestartExplorerShell();
 					break;
 			}
+
+			return OperationResult.Success;
 		}
 
 		private void CreateNewDesktop()
 		{
-			originalDesktop = desktopFactory.GetCurrent();
+			OriginalDesktop = desktopFactory.GetCurrent();
-			logger.Info($"Current desktop is {originalDesktop}.");
+			logger.Info($"Current desktop is {OriginalDesktop}.");
 
-			newDesktop = desktopFactory.CreateNew(nameof(SafeExamBrowser));
+			NewDesktop = desktopFactory.CreateNew(nameof(SafeExamBrowser));
-			logger.Info($"Created new desktop {newDesktop}.");
+			logger.Info($"Created new desktop {NewDesktop}.");
 
-			newDesktop.Activate();
+			NewDesktop.Activate();
-			processFactory.StartupDesktop = newDesktop;
+			processFactory.StartupDesktop = NewDesktop;
 			logger.Info("Successfully activated new desktop.");
 
 			explorerShell.Suspend();
@@ -117,21 +124,21 @@ namespace SafeExamBrowser.Runtime.Operations
 
 		private void CloseNewDesktop()
 		{
-			if (originalDesktop != null)
+			if (OriginalDesktop != null)
 			{
-				originalDesktop.Activate();
+				OriginalDesktop.Activate();
-				processFactory.StartupDesktop = originalDesktop;
+				processFactory.StartupDesktop = OriginalDesktop;
-				logger.Info($"Switched back to original desktop {originalDesktop}.");
+				logger.Info($"Switched back to original desktop {OriginalDesktop}.");
 			}
 			else
 			{
 				logger.Warn($"No original desktop found when attempting to close new desktop!");
 			}
 
-			if (newDesktop != null)
+			if (NewDesktop != null)
 			{
-				newDesktop.Close();
+				NewDesktop.Close();
-				logger.Info($"Closed new desktop {newDesktop}.");
+				logger.Info($"Closed new desktop {NewDesktop}.");
 			}
 			else
 			{

SafeExamBrowser.Runtime/Operations/KioskModeTerminationOperation.cs

@@ -0,0 +1,61 @@
+/*
+ * Copyright (c) 2018 ETH Zürich, Educational Development and Technology (LET)
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+using SafeExamBrowser.Contracts.Configuration;
+using SafeExamBrowser.Contracts.Configuration.Settings;
+using SafeExamBrowser.Contracts.Core.OperationModel;
+using SafeExamBrowser.Contracts.Logging;
+using SafeExamBrowser.Contracts.WindowsApi;
+
+namespace SafeExamBrowser.Runtime.Operations
+{
+	internal class KioskModeTerminationOperation : KioskModeOperation, IRepeatableOperation
+	{
+		private IConfigurationRepository configuration;
+		private KioskMode kioskMode;
+		private ILogger logger;
+
+		public KioskModeTerminationOperation(
+			IConfigurationRepository configuration,
+			IDesktopFactory desktopFactory,
+			IExplorerShell explorerShell,
+			ILogger logger,
+			IProcessFactory processFactory) : base(configuration, desktopFactory, explorerShell, logger, processFactory)
+		{
+			this.configuration = configuration;
+			this.logger = logger;
+		}
+
+		public override OperationResult Perform()
+		{
+			kioskMode = configuration.CurrentSettings.KioskMode;
+
+			return OperationResult.Success;
+		}
+
+		public override OperationResult Repeat()
+		{
+			var oldMode = kioskMode;
+			var newMode = configuration.CurrentSettings.KioskMode;
+
+			if (newMode == oldMode)
+			{
+				logger.Info($"New kiosk mode '{newMode}' is equal to the currently active '{oldMode}', skipping termination...");
+
+				return OperationResult.Success;
+			}
+
+			return base.Revert();
+		}
+
+		public override OperationResult Revert()
+		{
+			return OperationResult.Success;
+		}
+	}
+}

SafeExamBrowser.Runtime/Operations/ServiceOperation.cs

@@ -16,7 +16,7 @@ using SafeExamBrowser.Contracts.Logging;
 
 namespace SafeExamBrowser.Runtime.Operations
 {
-	internal class ServiceOperation : IOperation
+	internal class ServiceOperation : IRepeatableOperation
 	{
 		private bool connected, mandatory;
 		private IConfigurationRepository configuration;
@@ -43,7 +43,7 @@ namespace SafeExamBrowser.Runtime.Operations
 
 			if (mandatory && !connected)
 			{
-				logger.Error("Aborting startup because the service is mandatory but not available!");
+				logger.Error("Failed to initialize a service session since the service is mandatory but not available!");
 
 				return OperationResult.Failed;
 			}
@@ -61,17 +61,17 @@ namespace SafeExamBrowser.Runtime.Operations
 
 		public OperationResult Repeat()
 		{
-			// TODO: Re-check if mandatory, if so, try to connect (if not connected) - otherwise, no action required (except maybe logging of status?)
+			var result = Revert();
-			if (connected)
+
+			if (result != OperationResult.Success)
 			{
-				StopServiceSession();
+				return result;
-				StartServiceSession();
 			}
 
-			return OperationResult.Success;
+			return Perform();
 		}
 
-		public void Revert()
+		public OperationResult Revert()
 		{
 			logger.Info("Finalizing service session...");
 			StatusChanged?.Invoke(TextKey.OperationStatus_FinalizeServiceSession);
@@ -91,6 +91,8 @@ namespace SafeExamBrowser.Runtime.Operations
 					logger.Error("Failed to disconnect from the service!");
 				}
 			}
+
+			return OperationResult.Success;
 		}
 
 		private void StartServiceSession()

SafeExamBrowser.Runtime/Operations/SessionInitializationOperation.cs

@@ -15,7 +15,7 @@ using SafeExamBrowser.Contracts.Logging;
 
 namespace SafeExamBrowser.Runtime.Operations
 {
-	internal class SessionInitializationOperation : IOperation
+	internal class SessionInitializationOperation : IRepeatableOperation
 	{
 		private IConfigurationRepository configuration;
 		private ILogger logger;
@@ -40,14 +40,12 @@ namespace SafeExamBrowser.Runtime.Operations
 
 		public OperationResult Repeat()
 		{
-			InitializeSessionConfiguration();
+			return Perform();
-
-			return OperationResult.Success;
 		}
 
-		public void Revert()
+		public OperationResult Revert()
 		{
-			// Nothing to do here...
+			return OperationResult.Success;
 		}
 
 		private void InitializeSessionConfiguration()

SafeExamBrowser.Runtime/RuntimeController.cs

@@ -35,7 +35,7 @@ namespace SafeExamBrowser.Runtime
 		private ILogger logger;
 		private IMessageBox messageBox;
 		private IOperationSequence bootstrapSequence;
-		private IOperationSequence sessionSequence;
+		private IRepeatableOperationSequence sessionSequence;
 		private IRuntimeHost runtimeHost;
 		private IRuntimeWindow runtimeWindow;
 		private IServiceProxy service;
@@ -50,7 +50,7 @@ namespace SafeExamBrowser.Runtime
 			ILogger logger,
 			IMessageBox messageBox,
 			IOperationSequence bootstrapSequence,
-			IOperationSequence sessionSequence,
+			IRepeatableOperationSequence sessionSequence,
 			IRuntimeHost runtimeHost,
 			IServiceProxy service,
 			Action shutdown,
@@ -127,7 +127,7 @@ namespace SafeExamBrowser.Runtime
 			logger.Log(string.Empty);
 			logger.Info("Initiating shutdown procedure...");
 
-			var success = bootstrapSequence.TryRevert();
+			var success = bootstrapSequence.TryRevert() == OperationResult.Success;
 
 			if (success)
 			{
@@ -181,8 +181,8 @@ namespace SafeExamBrowser.Runtime
 
 				if (result == OperationResult.Failed)
 				{
-					// TODO: Check if message box is rendered on new desktop as well! -> E.g. if settings for reconfiguration are invalid
+					// TODO: Find solution for this; maybe manually switch back to original desktop?
-					messageBox.Show(TextKey.MessageBox_SessionStartError, TextKey.MessageBox_SessionStartErrorTitle, icon: MessageBoxIcon.Error, parent: runtimeWindow);
+					// messageBox.Show(TextKey.MessageBox_SessionStartError, TextKey.MessageBox_SessionStartErrorTitle, icon: MessageBoxIcon.Error, parent: runtimeWindow);
 
 					if (!initial)
 					{
@@ -202,7 +202,7 @@ namespace SafeExamBrowser.Runtime
 
 			DeregisterSessionEvents();
 
-			var success = sessionSequence.TryRevert();
+			var success = sessionSequence.TryRevert() == OperationResult.Success;
 
 			if (success)
 			{
@@ -235,38 +235,21 @@ namespace SafeExamBrowser.Runtime
 		}
 
 		private void DeregisterSessionEvents()
+		{
+			if (configuration.CurrentSession.ClientProcess != null)
 			{
 				configuration.CurrentSession.ClientProcess.Terminated -= ClientProcess_Terminated;
+			}
+
+			if (configuration.CurrentSession.ClientProxy != null)
+			{
 				configuration.CurrentSession.ClientProxy.ConnectionLost -= Client_ConnectionLost;
 			}
+		}
 
 		private void BootstrapSequence_ProgressChanged(ProgressChangedEventArgs args)
 		{
-			// TODO: Duplicated code (for splashScreen as well as runtimeWindow)!
+			MapProgress(splashScreen, args);
-			if (args.CurrentValue.HasValue)
-			{
-				splashScreen?.SetValue(args.CurrentValue.Value);
-			}
-
-			if (args.IsIndeterminate == true)
-			{
-				splashScreen?.SetIndeterminate();
-			}
-
-			if (args.MaxValue.HasValue)
-			{
-				splashScreen?.SetMaxValue(args.MaxValue.Value);
-			}
-
-			if (args.Progress == true)
-			{
-				splashScreen?.Progress();
-			}
-
-			if (args.Regress == true)
-			{
-				splashScreen?.Regress();
-			}
 		}
 
 		private void BootstrapSequence_StatusChanged(TextKey status)
@@ -277,7 +260,12 @@ namespace SafeExamBrowser.Runtime
 		private void ClientProcess_Terminated(int exitCode)
 		{
 			logger.Error($"Client application has unexpectedly terminated with exit code {exitCode}!");
-			// TODO: Check if message box is rendered on new desktop as well -> otherwise shutdown is blocked! Check if parent needed!
+
+			if (sessionRunning)
+			{
+				StopSession();
+			}
+
 			messageBox.Show(TextKey.MessageBox_ApplicationError, TextKey.MessageBox_ApplicationErrorTitle, icon: MessageBoxIcon.Error);
 
 			shutdown.Invoke();
@@ -286,7 +274,12 @@ namespace SafeExamBrowser.Runtime
 		private void Client_ConnectionLost()
 		{
 			logger.Error("Lost connection to the client application!");
-			// TODO: Check if message box is rendered on new desktop as well -> otherwise shutdown is blocked! Check if parent needed!
+
+			if (sessionRunning)
+			{
+				StopSession();
+			}
+
 			messageBox.Show(TextKey.MessageBox_ApplicationError, TextKey.MessageBox_ApplicationErrorTitle, icon: MessageBoxIcon.Error);
 
 			shutdown.Invoke();
@@ -400,35 +393,40 @@ namespace SafeExamBrowser.Runtime
 
 		private void SessionSequence_ProgressChanged(ProgressChangedEventArgs args)
 		{
-			if (args.CurrentValue.HasValue)
+			MapProgress(runtimeWindow, args);
-			{
-				runtimeWindow?.SetValue(args.CurrentValue.Value);
-			}
-
-			if (args.IsIndeterminate == true)
-			{
-				runtimeWindow?.SetIndeterminate();
-			}
-
-			if (args.MaxValue.HasValue)
-			{
-				runtimeWindow?.SetMaxValue(args.MaxValue.Value);
-			}
-
-			if (args.Progress == true)
-			{
-				runtimeWindow?.Progress();
-			}
-
-			if (args.Regress == true)
-			{
-				runtimeWindow?.Regress();
-			}
 		}
 
 		private void SessionSequence_StatusChanged(TextKey status)
 		{
 			runtimeWindow?.UpdateStatus(status, true);
 		}
+
+		private void MapProgress(IProgressIndicator progressIndicator, ProgressChangedEventArgs args)
+		{
+			if (args.CurrentValue.HasValue)
+			{
+				progressIndicator?.SetValue(args.CurrentValue.Value);
+			}
+
+			if (args.IsIndeterminate == true)
+			{
+				progressIndicator?.SetIndeterminate();
+			}
+
+			if (args.MaxValue.HasValue)
+			{
+				progressIndicator?.SetMaxValue(args.MaxValue.Value);
+			}
+
+			if (args.Progress == true)
+			{
+				progressIndicator?.Progress();
+			}
+
+			if (args.Regress == true)
+			{
+				progressIndicator?.Regress();
+			}
+		}
 	}
 }

SafeExamBrowser.Runtime/SafeExamBrowser.Runtime.csproj

@@ -92,6 +92,7 @@
     <Compile Include="Operations\Events\ConfigurationCompletedEventArgs.cs" />
     <Compile Include="Operations\Events\PasswordRequiredEventArgs.cs" />
     <Compile Include="Operations\KioskModeOperation.cs" />
+    <Compile Include="Operations\KioskModeTerminationOperation.cs" />
     <Compile Include="Operations\ServiceOperation.cs" />
     <Compile Include="Operations\SessionInitializationOperation.cs" />
     <Compile Include="Communication\ProxyFactory.cs" />