Index: Core/Common/test/Core.Common.Gui.Test/GuiCoreTest.cs
===================================================================
diff -u -rc063a97260cc4d630a453c359d49fca96ed8ac80 -r761d4c23b5c98c87caa9a94d14b41074c862c425
--- Core/Common/test/Core.Common.Gui.Test/GuiCoreTest.cs	(.../GuiCoreTest.cs)	(revision c063a97260cc4d630a453c359d49fca96ed8ac80)
+++ Core/Common/test/Core.Common.Gui.Test/GuiCoreTest.cs	(.../GuiCoreTest.cs)	(revision 761d4c23b5c98c87caa9a94d14b41074c862c425)
@@ -34,6 +34,7 @@
 using Core.Common.Gui.ContextMenu;
 using Core.Common.Gui.Forms.MainWindow;
 using Core.Common.Gui.Forms.MessageWindow;
+using Core.Common.Gui.Forms.ProjectExplorer;
 using Core.Common.Gui.Forms.PropertyGridView;
 using Core.Common.Gui.Forms.ViewHost;
 using Core.Common.Gui.Plugin;
@@ -417,6 +418,7 @@
             {
                 using (var gui = new GuiCore(new MainWindow(), projectStore, projectMigrator, projectFactory, new GuiCoreSettings()))
                 {
+                    gui.Plugins.Add(new TestPlugin());
                     gui.Run();
 
                     // Precondition:
@@ -454,6 +456,7 @@
             using (var toolView = new TestView())
             using (var gui = new GuiCore(new MainWindow(), projectStore, projectMigrator, projectFactory, new GuiCoreSettings()))
             {
+                gui.Plugins.Add(new TestPlugin());
                 gui.Run();
 
                 gui.ViewHost.AddToolView(toolView, ToolViewLocation.Left);
@@ -483,6 +486,7 @@
             using (var documentView = new TestView())
             using (var gui = new GuiCore(new MainWindow(), projectStore, projectMigrator, projectFactory, new GuiCoreSettings()))
             {
+                gui.Plugins.Add(new TestPlugin());
                 gui.Run();
 
                 gui.ViewHost.AddDocumentView(documentView);
@@ -518,6 +522,8 @@
             {
                 using (var gui = new GuiCore(new MainWindow(), projectStore, projectMigrator, projectFactory, new GuiCoreSettings()))
                 {
+                    gui.Plugins.Add(new TestPlugin());
+                    
                     // Call
                     gui.Run();
 
@@ -566,6 +572,8 @@
             {
                 using (var gui = new GuiCore(new MainWindow(), projectStore, projectMigrator, projectFactory, new GuiCoreSettings()))
                 {
+                    gui.Plugins.Add(new TestPlugin());
+
                     // Call
                     gui.Run();
 
@@ -615,6 +623,8 @@
             using (var mainWindow = new MainWindow())
             using (var gui = new GuiCore(mainWindow, projectStore, projectMigrator, projectFactory, fixedSettings))
             {
+                gui.Plugins.Add(new TestPlugin());
+                
                 // Call
                 void Call() => gui.Run(testFile);
 
@@ -669,6 +679,8 @@
             using (var mainWindow = new MainWindow())
             using (var gui = new GuiCore(mainWindow, projectStore, projectMigrator, projectFactory, fixedSettings))
             {
+                gui.Plugins.Add(new TestPlugin());
+                
                 // Call
                 gui.Run(testFile);
 
@@ -714,6 +726,8 @@
             using (var mainWindow = new MainWindow())
             using (var gui = new GuiCore(mainWindow, projectStore, projectMigrator, projectFactory, fixedSettings))
             {
+                gui.Plugins.Add(new TestPlugin());
+                
                 // Call
                 void Call() => gui.Run(testFile);
 
@@ -764,6 +778,8 @@
             using (var mainWindow = new MainWindow())
             using (var gui = new GuiCore(mainWindow, projectStore, projectMigrator, projectFactory, fixedSettings))
             {
+                gui.Plugins.Add(new TestPlugin());
+                
                 // Call
                 void Call() => gui.Run(testFile);
 
@@ -815,6 +831,8 @@
             using (var mainWindow = new MainWindow())
             using (var gui = new GuiCore(mainWindow, projectStore, projectMigrator, projectFactory, fixedSettings))
             {
+                gui.Plugins.Add(new TestPlugin());
+                
                 // Call
                 void Call() => gui.Run(testFile);
 
@@ -862,6 +880,8 @@
             using (var mainWindow = new MainWindow())
             using (var gui = new GuiCore(mainWindow, projectStore, projectMigrator, projectFactory, fixedSettings))
             {
+                gui.Plugins.Add(new TestPlugin());
+                
                 // Call
                 gui.Run(path);
 
@@ -882,18 +902,13 @@
             var mocks = new MockRepository();
             var projectStore = mocks.Stub<IStoreProject>();
             var projectMigrator = mocks.Stub<IMigrateProject>();
-            var plugin = mocks.Stub<PluginBase>();
-            plugin.Stub(p => p.Deactivate());
-            plugin.Stub(p => p.Dispose());
-            plugin.Expect(p => p.Activate());
-            plugin.Expect(p => p.GetViewInfos()).Return(Enumerable.Empty<ViewInfo>());
-            plugin.Expect(p => p.GetPropertyInfos()).Return(Enumerable.Empty<PropertyInfo>());
             IProjectFactory projectFactory = CreateProjectFactory(mocks);
             mocks.ReplayAll();
 
             // Setup
             using (var gui = new GuiCore(new MainWindow(), projectStore, projectMigrator, projectFactory, new GuiCoreSettings()))
             {
+                var plugin = new TestPlugin();
                 gui.Plugins.Add(plugin);
 
                 // Call
@@ -916,6 +931,10 @@
             var plugin = mocks.Stub<PluginBase>();
             plugin.Stub(p => p.GetViewInfos()).Return(Enumerable.Empty<ViewInfo>());
             plugin.Stub(p => p.GetPropertyInfos()).Return(Enumerable.Empty<PropertyInfo>());
+            plugin.Stub(p => p.GetTreeNodeInfos()).Return(new TreeNodeInfo[]
+            {
+                new TreeNodeInfo<IProject>()
+            });
             plugin.Stub(p => p.Activate()).Throw(new Exception("ERROR!"));
             plugin.Expect(p => p.Deactivate());
             plugin.Expect(p => p.Dispose());
@@ -945,6 +964,10 @@
             var plugin = mocks.Stub<PluginBase>();
             plugin.Stub(p => p.GetViewInfos()).Return(Enumerable.Empty<ViewInfo>());
             plugin.Stub(p => p.GetPropertyInfos()).Return(Enumerable.Empty<PropertyInfo>());
+            plugin.Stub(p => p.GetTreeNodeInfos()).Return(new TreeNodeInfo[]
+            {
+                new TreeNodeInfo<IProject>()
+            });
             plugin.Stub(p => p.Activate()).Throw(new Exception("ERROR!"));
             plugin.Stub(p => p.Deactivate()).Throw(new Exception("MORE ERROR!"));
             plugin.Expect(p => p.Dispose());
@@ -981,14 +1004,17 @@
 
             using (var gui = new GuiCore(new MainWindow(), projectStore, projectMigrator, projectFactory, new GuiCoreSettings()))
             {
+                gui.Plugins.Add(new TestPlugin());
+                
                 // Call
                 gui.Run();
 
                 // Assert
                 CollectionAssert.IsEmpty(gui.ViewHost.DocumentViews);
                 Assert.IsNull(gui.ViewHost.ActiveDocumentView);
 
-                Assert.AreEqual(2, gui.ViewHost.ToolViews.Count());
+                Assert.AreEqual(3, gui.ViewHost.ToolViews.Count());
+                Assert.AreEqual(1, gui.ViewHost.ToolViews.Count(v => v is ProjectExplorer));
                 Assert.AreEqual(1, gui.ViewHost.ToolViews.Count(v => v is PropertyGridView));
                 Assert.AreEqual(1, gui.ViewHost.ToolViews.Count(v => v is MessageWindow));
 
@@ -1253,6 +1279,7 @@
             using (var treeView = new TreeViewControl())
             using (var gui = new GuiCore(new MainWindow(), projectStore, projectMigrator, projectFactory, new GuiCoreSettings()))
             {
+                gui.Plugins.Add(new TestPlugin());
                 gui.Run();
 
                 // Call
@@ -1330,6 +1357,7 @@
 
             using (var gui = new GuiCore(new MainWindow(), projectStore, projectMigrator, projectFactory, new GuiCoreSettings()))
             {
+                gui.Plugins.Add(new TestPlugin());
                 gui.Run();
                 gui.ViewHost.AddDocumentView(selectionProvider);
 
@@ -1361,6 +1389,7 @@
 
             using (var gui = new GuiCore(new MainWindow(), projectStore, projectMigrator, projectFactory, new GuiCoreSettings()))
             {
+                gui.Plugins.Add(new TestPlugin());
                 gui.Run();
                 gui.ViewHost.AddDocumentView(selectionProvider);
 
@@ -1391,6 +1420,7 @@
 
             using (var gui = new GuiCore(new MainWindow(), projectStore, projectMigrator, projectFactory, new GuiCoreSettings()))
             {
+                gui.Plugins.Add(new TestPlugin());
                 gui.Run();
                 gui.ViewHost.AddDocumentView(selectionProvider);
                 SetActiveView((AvalonDockViewHost) gui.ViewHost, selectionProvider);
@@ -1423,6 +1453,7 @@
 
             using (var gui = new GuiCore(new MainWindow(), projectStore, projectMigrator, projectFactory, new GuiCoreSettings()))
             {
+                gui.Plugins.Add(new TestPlugin());
                 gui.Run();
                 gui.ViewHost.AddDocumentView(selectionProvider);
                 SetActiveView((AvalonDockViewHost) gui.ViewHost, selectionProvider);
@@ -1457,6 +1488,7 @@
 
             using (var gui = new GuiCore(new MainWindow(), projectStore, projectMigrator, projectFactory, new GuiCoreSettings()))
             {
+                gui.Plugins.Add(new TestPlugin());
                 gui.Run();
                 gui.ViewHost.AddDocumentView(testView);
 
@@ -1488,6 +1520,7 @@
 
             using (var gui = new GuiCore(new MainWindow(), projectStore, projectMigrator, projectFactory, new GuiCoreSettings()))
             {
+                gui.Plugins.Add(new TestPlugin());
                 gui.Run();
                 gui.ViewHost.AddDocumentView(testView);
 
@@ -1518,6 +1551,7 @@
 
             using (var gui = new GuiCore(new MainWindow(), projectStore, projectMigrator, projectFactory, new GuiCoreSettings()))
             {
+                gui.Plugins.Add(new TestPlugin());
                 gui.Run();
                 gui.ViewHost.AddDocumentView(selectionProvider);
                 SetActiveView((AvalonDockViewHost) gui.ViewHost, selectionProvider);
@@ -1550,6 +1584,7 @@
 
             using (var gui = new GuiCore(new MainWindow(), projectStore, projectMigrator, projectFactory, new GuiCoreSettings()))
             {
+                gui.Plugins.Add(new TestPlugin());
                 gui.Run();
                 gui.ViewHost.AddDocumentView(selectionProvider);
                 SetActiveView((AvalonDockViewHost) gui.ViewHost, selectionProvider);
Index: Core/Common/test/Core.Common.Integration.Test/Riskeer/Application.Riskeer/GuiCoreIntegrationTest.cs
===================================================================
diff -u -r4b9e28a28b8004dc9dfca896c32e2a21c10a2405 -r761d4c23b5c98c87caa9a94d14b41074c862c425
--- Core/Common/test/Core.Common.Integration.Test/Riskeer/Application.Riskeer/GuiCoreIntegrationTest.cs	(.../GuiCoreIntegrationTest.cs)	(revision 4b9e28a28b8004dc9dfca896c32e2a21c10a2405)
+++ Core/Common/test/Core.Common.Integration.Test/Riskeer/Application.Riskeer/GuiCoreIntegrationTest.cs	(.../GuiCoreIntegrationTest.cs)	(revision 761d4c23b5c98c87caa9a94d14b41074c862c425)
@@ -19,6 +19,7 @@
 // Stichting Deltares and remain full property of Stichting Deltares at all times.
 // All rights reserved.
 
+using System;
 using System.Threading;
 using System.Windows.Controls;
 using System.Windows.Threading;
@@ -30,6 +31,7 @@
 using Core.Common.TestUtil;
 using NUnit.Framework;
 using Rhino.Mocks;
+using Riskeer.Integration.Data;
 using Riskeer.Integration.Plugin;
 
 namespace Core.Common.Integration.Test.Riskeer.Application.Riskeer
@@ -57,7 +59,7 @@
             var projectStore = mocks.Stub<IStoreProject>();
             var projectMigrator = mocks.Stub<IMigrateProject>();
             var projectFactory = mocks.Stub<IProjectFactory>();
-            projectFactory.Stub(pf => pf.CreateNewProject()).Return(mocks.Stub<IProject>());
+            projectFactory.Stub(pf => pf.CreateNewProject()).Return(new RiskeerProject());
             mocks.ReplayAll();
 
             using (var gui = new GuiCore(new MainWindow(), projectStore, projectMigrator, projectFactory, new GuiCoreSettings()))
@@ -73,35 +75,38 @@
         [Apartment(ApartmentState.STA)]
         public void Run_StartWithCommonPlugins_RunsFasterThanThreshold()
         {
-            TestHelper.AssertIsFasterThan(7500, StartWithCommonPlugins);
-        }
-
-        [Test]
-        [Apartment(ApartmentState.STA)]
-        public void FormActionIsRunForMainWindow()
-        {
-            //testing testhelper + visible changed event of mainwindow.
-            //could be tested separately but the combination is vital to many tests. That's why this test is here.
+            // Setup
             var mocks = new MockRepository();
             var projectStore = mocks.Stub<IStoreProject>();
             var projectMigrator = mocks.Stub<IMigrateProject>();
             var projectFactory = mocks.Stub<IProjectFactory>();
-            projectFactory.Stub(pf => pf.CreateNewProject()).Return(mocks.Stub<IProject>());
+            projectFactory.Stub(pf => pf.CreateNewProject()).Return(new RiskeerProject());
             mocks.ReplayAll();
 
             using (var gui = new GuiCore(new MainWindow(), projectStore, projectMigrator, projectFactory, new GuiCoreSettings()))
             {
-                gui.Run();
-                var callCount = 0;
-                WpfTestHelper.ShowModal((Control) gui.MainWindow, () => callCount++);
-                Assert.AreEqual(1, callCount);
+                gui.Plugins.Add(new RiskeerPlugin());
+
+                // Call
+                void Action()
+                {
+                    gui.Run();
+                    WpfTestHelper.ShowModal((Control) gui.MainWindow);
+                }
+
+                // Assert
+                TestHelper.AssertIsFasterThan(7500, Action);
             }
 
             mocks.VerifyAll();
         }
 
-        private static void StartWithCommonPlugins()
+        [Test]
+        [Apartment(ApartmentState.STA)]
+        public void FormActionIsRunForMainWindow()
         {
+            //testing testhelper + visible changed event of mainwindow.
+            //could be tested separately but the combination is vital to many tests. That's why this test is here.
             var mocks = new MockRepository();
             var projectStore = mocks.Stub<IStoreProject>();
             var projectMigrator = mocks.Stub<IMigrateProject>();
@@ -111,11 +116,12 @@
 
             using (var gui = new GuiCore(new MainWindow(), projectStore, projectMigrator, projectFactory, new GuiCoreSettings()))
             {
-                gui.Plugins.Add(new RiskeerPlugin());
-
+                gui.Plugins.Add(new TestPlugin());
                 gui.Run();
-
-                WpfTestHelper.ShowModal((Control) gui.MainWindow);
+                
+                var callCount = 0;
+                WpfTestHelper.ShowModal((Control) gui.MainWindow, () => callCount++);
+                Assert.AreEqual(1, callCount);
             }
 
             mocks.VerifyAll();
Index: Core/Common/test/Core.Common.TestUtil/TestPlugin.cs
===================================================================
diff -u
--- Core/Common/test/Core.Common.TestUtil/TestPlugin.cs	(revision 0)
+++ Core/Common/test/Core.Common.TestUtil/TestPlugin.cs	(revision 761d4c23b5c98c87caa9a94d14b41074c862c425)
@@ -0,0 +1,39 @@
+// Copyright (C) Stichting Deltares 2021. All rights reserved.
+//
+// This file is part of Riskeer.
+//
+// Riskeer is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+// 
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with this program. If not, see <http://www.gnu.org/licenses/>.
+//
+// All names, logos, and references to "Deltares" are registered trademarks of
+// Stichting Deltares and remain full property of Stichting Deltares at all times.
+// All rights reserved.
+
+using System.Collections.Generic;
+using Core.Common.Base.Data;
+using Core.Common.Controls.TreeView;
+using Core.Common.Gui.Plugin;
+
+namespace Core.Common.TestUtil
+{
+    /// <summary>
+    /// Simple plugin that can be used in tests.
+    /// </summary>
+    public class TestPlugin : PluginBase
+    {
+        public override IEnumerable<TreeNodeInfo> GetTreeNodeInfos()
+        {
+            yield return new TreeNodeInfo<IProject>();
+        }
+    }
+}
\ No newline at end of file
Index: Core/Plugins/test/Core.Plugins.Chart.Test/ChartPluginTest.cs
===================================================================
diff -u -r1b53b144acc8a3a2826b63f0d841e4c123a8b461 -r761d4c23b5c98c87caa9a94d14b41074c862c425
--- Core/Plugins/test/Core.Plugins.Chart.Test/ChartPluginTest.cs	(.../ChartPluginTest.cs)	(revision 1b53b144acc8a3a2826b63f0d841e4c123a8b461)
+++ Core/Plugins/test/Core.Plugins.Chart.Test/ChartPluginTest.cs	(.../ChartPluginTest.cs)	(revision 761d4c23b5c98c87caa9a94d14b41074c862c425)
@@ -31,6 +31,7 @@
 using Core.Common.Gui.Plugin;
 using Core.Common.Gui.Settings;
 using Core.Common.Gui.TestUtil;
+using Core.Common.TestUtil;
 using Core.Common.Util.Reflection;
 using Core.Components.Chart.Data;
 using Core.Components.Chart.Forms;
@@ -172,6 +173,7 @@
                     Gui = gui
                 };
 
+                gui.Plugins.Add(new TestPlugin());
                 gui.Plugins.Add(plugin);
                 gui.Run();
 
@@ -212,6 +214,7 @@
                     Gui = gui
                 };
 
+                gui.Plugins.Add(new TestPlugin());
                 gui.Plugins.Add(plugin);
                 gui.Run();
 
@@ -256,6 +259,7 @@
                     Gui = gui
                 };
 
+                gui.Plugins.Add(new TestPlugin());
                 gui.Plugins.Add(plugin);
                 gui.Run();
 
@@ -298,6 +302,7 @@
                     Gui = gui
                 };
 
+                gui.Plugins.Add(new TestPlugin());
                 gui.Plugins.Add(plugin);
                 gui.Run();
 
Index: Core/Plugins/test/Core.Plugins.Map.Test/MapPluginTest.cs
===================================================================
diff -u -r1b53b144acc8a3a2826b63f0d841e4c123a8b461 -r761d4c23b5c98c87caa9a94d14b41074c862c425
--- Core/Plugins/test/Core.Plugins.Map.Test/MapPluginTest.cs	(.../MapPluginTest.cs)	(revision 1b53b144acc8a3a2826b63f0d841e4c123a8b461)
+++ Core/Plugins/test/Core.Plugins.Map.Test/MapPluginTest.cs	(.../MapPluginTest.cs)	(revision 761d4c23b5c98c87caa9a94d14b41074c862c425)
@@ -31,6 +31,7 @@
 using Core.Common.Gui.Plugin;
 using Core.Common.Gui.Settings;
 using Core.Common.Gui.TestUtil;
+using Core.Common.TestUtil;
 using Core.Common.Util.Reflection;
 using Core.Components.DotSpatial.Forms;
 using Core.Components.Gis.Forms;
@@ -176,6 +177,7 @@
 
             using (var gui = new GuiCore(new MainWindow(), projectStore, projectMigrator, projectFactory, new GuiCoreSettings()))
             {
+                gui.Plugins.Add(new TestPlugin());
                 gui.Plugins.Add(new MapPlugin
                 {
                     Gui = gui
@@ -219,6 +221,7 @@
                     Gui = gui
                 };
 
+                gui.Plugins.Add(new TestPlugin());
                 gui.Plugins.Add(plugin);
                 gui.Run();
 
@@ -259,6 +262,7 @@
                     Gui = gui
                 };
 
+                gui.Plugins.Add(new TestPlugin());
                 gui.Plugins.Add(plugin);
                 gui.Run();
 
@@ -303,6 +307,7 @@
                     Gui = gui
                 };
 
+                gui.Plugins.Add(new TestPlugin());
                 gui.Plugins.Add(plugin);
                 gui.Run();
 
@@ -345,6 +350,7 @@
                     Gui = gui
                 };
 
+                gui.Plugins.Add(new TestPlugin());
                 gui.Plugins.Add(plugin);
                 gui.Run();
 
Index: Riskeer/Storage/test/Riskeer.Storage.Core.Test/IntegrationTests/StorageSqLiteIntegrationTest.cs
===================================================================
diff -u -rda1df87d94dcc61aa26d5f033c6bf579c2249cdd -r761d4c23b5c98c87caa9a94d14b41074c862c425
--- Riskeer/Storage/test/Riskeer.Storage.Core.Test/IntegrationTests/StorageSqLiteIntegrationTest.cs	(.../StorageSqLiteIntegrationTest.cs)	(revision da1df87d94dcc61aa26d5f033c6bf579c2249cdd)
+++ Riskeer/Storage/test/Riskeer.Storage.Core.Test/IntegrationTests/StorageSqLiteIntegrationTest.cs	(.../StorageSqLiteIntegrationTest.cs)	(revision 761d4c23b5c98c87caa9a94d14b41074c862c425)
@@ -181,6 +181,8 @@
 
             using (var gui = new GuiCore(new MainWindow(), projectStore, projectMigrator, new RiskeerProjectFactory(), new GuiCoreSettings()))
             {
+                gui.Plugins.Add(new TestPlugin());
+                
                 // When
                 gui.Run(testFile);
 
@@ -218,6 +220,8 @@
 
             using (var gui = new GuiCore(new MainWindow(), projectStore, projectMigrator, new RiskeerProjectFactory(), new GuiCoreSettings()))
             {
+                gui.Plugins.Add(new TestPlugin());
+                
                 // When
                 void Action() => gui.Run(projectFilePath);