Make sure we never blow up in release mode

Tests in debug mode will signal invalid method calls. We might need to
run tests in debug and release mode in the buildbot so we're sure we
catch all the problems.

Author: shana

src/GitHub.App/Controllers/UIController.cs

@@ -156,7 +156,6 @@ void End(bool success)
             completion?.OnNext(success);
             completion?.OnCompleted();
             transition.OnCompleted();
-            completion = null;
         }
 
         void RunView(UIViewType viewType)

src/GitHub.VisualStudio/Services/UIProvider.cs

@@ -31,7 +31,6 @@ public class UIProvider : IUIProvider, IDisposable
         CompositionContainer tempContainer;
         readonly Dictionary<string, ComposablePart> tempParts;
         ExportLifetimeContext<IUIController> currentUIFlow;
-        IUIController currentUI;
         readonly Version currentVersion;
         bool initializingLogging = false;
 
@@ -202,9 +201,9 @@ public IObservable<UserControl> SetupUI(UIControllerFlow controllerFlow, [AllowN
 
             var factory = GetService<IExportFactoryProvider>();
             currentUIFlow = factory.UIControllerFactory.CreateExport();
-            currentUI = currentUIFlow.Value;
             var disposable = currentUIFlow;
-            var creation = currentUI.SelectFlow(controllerFlow);
+            var ui = currentUIFlow.Value;
+            var creation = ui.SelectFlow(controllerFlow);
             windowController = new UI.WindowController(creation);
             windowController.WindowStartupLocation = System.Windows.WindowStartupLocation.CenterOwner;
             windowController.Closed += StopUIFlowWhenWindowIsClosedByUser;
@@ -217,14 +216,21 @@ public IObservable<UserControl> SetupUI(UIControllerFlow controllerFlow, [AllowN
                 else
                     StopUI();
             });
-            currentUI.Start(connection);
+            ui.Start(connection);
             return creation;
         }
 
         public IObservable<bool> ListenToCompletionState()
         {
-            Debug.Assert(currentUI != null, "Cannot call ListenToCompletionState without calling SetupUI first");
-            return currentUI?.ListenToCompletionState();
+            var ui = currentUIFlow?.Value;
+            if (ui == null)
+            {
+                log.Error("UIProvider:ListenToCompletionState:Cannot call ListenToCompletionState without calling SetupUI first");
+#if DEBUG
+                throw new InvalidOperationException("Cannot call ListenToCompletionState without calling SetupUI first");
+#endif
+            }
+            return ui?.ListenToCompletionState() ?? Observable.Return(false);
         }
 
         public void RunUI()
@@ -279,7 +285,6 @@ public void StopUI()
             }
 
             StopUI(currentUIFlow);
-            currentUI = null;
             currentUIFlow = null;
         }
 

src/UnitTests/GitHub.App/Controllers/UIProviderTests.cs

@@ -0,0 +1,38 @@
+using System;
+using System.ComponentModel.Composition;
+using System.Reactive.Linq;
+using System.Windows.Controls;
+using GitHub.Controllers;
+using GitHub.Models;
+using GitHub.Services;
+using GitHub.UI;
+using NSubstitute;
+using Xunit;
+using UnitTests;
+using GitHub.ViewModels;
+using ReactiveUI;
+using System.Collections.Generic;
+using GitHub.Authentication;
+using System.Collections.ObjectModel;
+using GitHub.VisualStudio;
+
+public class UIProviderTests : TestBaseClass
+{
+    [Fact]
+    public void ListenToCompletionDoesNotThrowInRelease()
+    {
+        var provider = Substitutes.GetFullyMockedServiceProvider();
+
+        using (var p = new UIProvider(provider))
+        {
+#if DEBUG
+            Assert.ThrowsAny<InvalidOperationException>(() =>
+            {
+#endif
+                p.ListenToCompletionState();
+#if DEBUG
+            });
+#endif
+        }
+    }
+}

src/UnitTests/UnitTests.csproj

@@ -139,6 +139,7 @@
     <Compile Include="GitHub.Api\SimpleApiClientTests.cs" />
     <Compile Include="GitHub.App\Caches\CredentialCacheTests.cs" />
     <Compile Include="GitHub.App\Caches\ImageCacheTests.cs" />
+    <Compile Include="GitHub.App\Controllers\UIProviderTests.cs" />
     <Compile Include="GitHub.App\Models\ModelServiceTests.cs" />
     <Compile Include="GitHub.App\Controllers\UIControllerTests.cs" />
     <Compile Include="GitHub.App\Models\PullRequestModelTests.cs" />