Don't add current page to current page.

When the page to be navigated to in the GitHub pane is the current page, do nothing.

Author: grokys

src/GitHub.App/ViewModels/GitHubPane/GitHubPaneViewModel.cs

@@ -122,7 +122,7 @@ public GitHubPaneViewModel(
                 .Subscribe(x => NavigateTo(x).Forget());
 
             this.WhenAnyValue(x => x.SearchQuery)
-                .Where(x => navigator.Content != null)
+                .Where(x => navigator.Content is ISearchablePageViewModel)
                 .ObserveOn(RxApp.MainThreadScheduler)
                 .Subscribe(x => ((ISearchablePageViewModel)navigator.Content).SearchQuery = x);
         }
@@ -280,7 +280,7 @@ OleMenuCommand BindNavigatorCommand<T>(IServiceProvider paneServiceProvider, int
         }
 
         async Task NavigateTo<TViewModel>(Func<TViewModel, Task> initialize, Func<TViewModel, bool> match = null)
-            where TViewModel : IPanePageViewModel
+            where TViewModel : class, IPanePageViewModel
         {
             Guard.ArgumentNotNull(initialize, nameof(initialize));
 
@@ -299,7 +299,7 @@ async Task NavigateTo<TViewModel>(Func<TViewModel, Task> initialize, Func<TViewM
                     navigator.NavigateTo(viewModel);
                     await initialize(viewModel);
                 }
-                else
+                else if (navigator.Content != viewModel)
                 {
                     navigator.NavigateTo(viewModel);
                 }

test/UnitTests/GitHub.App/ViewModels/GitHubPane/GitHubPaneViewModelTests.cs

@@ -148,6 +148,26 @@ public async Task HasNoEffectWhenUserLoggedOut()
 
             viewModelFactory.DidNotReceive().CreateViewModel<IPullRequestListViewModel>();
         }
+
+        [Fact]
+        public async Task HasNoEffectWhenAlreadyCurrentPage()
+        {
+            var te = CreateTeamExplorerServiceHolder(ValidGitHubRepo);
+            var cm = CreateConnectionManager(ValidGitHubRepo);
+            var nav = new NavigationViewModel();
+            var target = CreateTarget(
+                teServiceHolder: te,
+                connectionManager: cm,
+                navigator: nav);
+
+            await Initialize(target);
+            Assert.Same(nav, target.Content);
+            Assert.IsAssignableFrom<IPullRequestListViewModel>(nav.Content);
+
+            await target.ShowPullRequests();
+
+            Assert.Equal(1, nav.History.Count);
+        }
     }
 
     static GitHubPaneViewModel CreateTarget(