Hermetic real-MainWindow tests: LayoutPathOverride temp-DB seam (InternalsVisibleTo); fix tests persisting fake webcam sources over the real layout DB; LayoutStore delete-roundtrip guard

ViewModels/MainViewModel.cs

@@ -481,7 +481,7 @@ public class MainViewModel : ViewModelBase
         SaveLayoutAsCommand = new RelayCommand(_ => SaveLayoutAs());
         OpenLayoutCommand = new RelayCommand(_ => OpenLayoutFile());
 
-        _layoutStore = new LayoutStore(DefaultLayoutPath);
+        _layoutStore = new LayoutStore(LayoutPathOverride ?? DefaultLayoutPath);
         _activeLayoutPath = _layoutStore.ActivePath;
 
         _cameraEnumerator = new MediaCaptureCameraEnumerator();
@@ -531,6 +531,11 @@ public class MainViewModel : ViewModelBase
         "ytLlive",
         "ytLlive.db");
 
+    // Test seam: a real MainWindow test must never read or write the user's
+    // real layout DB (it would persist test sources over real ones). Tests set
+    // this to a temp path before constructing MainWindow and reset it after.
+    internal static string? LayoutPathOverride { get; set; }
+
     private void LoadLayout()
     {
         _isLoading = true;

ai.md

@@ -45,7 +45,25 @@ dotnet.exe vstest "C:\...\ytLive.Tests\bin\Debug\net8.0-windows10.0.19041.0\ytLi
 
 Good Dog Rule: ONE integration test per branch, ONE test per PR. Current: TokenStore DPAPI
 roundtrip/corrupt/missing/clear, OAuth exchange/refresh/ClearSession, CameraManager refcount +
-frame pump + failure handling (fakes for the WinRT seams) — 11 passing.
+frame pump + failure handling (fakes for the WinRT seams), real-`MainWindow` round-clip
+interaction test, LayoutStore delete roundtrip — 13 passing.
+
+### Real-MainWindow tests MUST be hermetic (DB pollution bug)
+
+The integration test boots a real `MainWindow` → `MainViewModel` → real `LayoutStore`
+(`%APPDATA%\ytLlive\ytLlive.db`). `Shutdown()` on close **saves the layout** (full rewrite:
+DELETE all scenes/sources, re-insert), so any source a test adds would be persisted over the
+user's real ones — this happened and wiped the real webcam source (DeviceId replaced by the
+test's fake `test-camera`). Rule: a test that constructs `MainWindow` MUST first set
+`MainViewModel.LayoutPathOverride` to a temp DB path and reset it (plus
+`SqliteConnection.ClearAllPools()` + delete) in `finally`. The seam is
+`internal static string? LayoutPathOverride` (line ~529 in `MainViewModel.cs`),
+`ytLive.csproj` has `InternalsVisibleTo("ytLive.Tests")`.
+
+The layout DB is a **full rewrite per save** (delete all, re-insert from memory), so
+save/load round trips are exact: a source removed in the UI (`RemoveSource` →
+`scene.Sources.Remove` → `OnSourcesChanged` → debounced `ScheduleSave`, plus `Shutdown` on
+close) does **not** come back after reload (`LayoutStorePersistenceTests` guards this).
 
 ## Architecture
 

ytLive.Tests/LayoutStorePersistenceTests.cs

@@ -0,0 +1,50 @@
+using System;
+using System.IO;
+using Microsoft.Data.Sqlite;
+using Xunit;
+using ytLive.Models;
+using ytLive.Services;
+
+namespace ytLive.Tests;
+
+/// <summary>
+/// The layout DB is a full rewrite on every save (DELETE all scenes/sources,
+/// re-insert from memory). This guards the round trip: sources the user deletes
+/// in the UI must not come back after a save + reload.
+/// </summary>
+public class LayoutStorePersistenceTests
+{
+    [Fact]
+    public void Deleted_Webcam_Source_Does_Not_Return_After_Save_And_Reload()
+    {
+        var path = Path.Combine(Path.GetTempPath(), $"ytLlive-layout-{Guid.NewGuid():N}.db");
+        try
+        {
+            using var store = new LayoutStore(path);
+            var scene = new Scene { Name = "Starting" };
+            scene.Sources.Add(new Source
+            {
+                Name = "Webcam",
+                Type = SourceType.Webcam,
+                DeviceId = "real-device",
+                Width = 480,
+                Height = 270,
+            });
+            store.Save(new[] { scene });
+
+            var reloaded = store.Load();
+            Assert.Single(reloaded[0].Sources);
+
+            reloaded[0].Sources.RemoveAt(0);
+            store.Save(reloaded);
+
+            var afterDelete = store.Load();
+            Assert.Empty(afterDelete[0].Sources);
+        }
+        finally
+        {
+            SqliteConnection.ClearAllPools();
+            try { File.Delete(path); } catch { /* best-effort cleanup */ }
+        }
+    }
+}

ytLive.Tests/RoundClipInteractionTests.cs

@@ -5,6 +5,7 @@ using System.Windows.Controls;
 using System.Windows.Media;
 using System.Windows.Shapes;
 using System.Windows.Threading;
+using Microsoft.Data.Sqlite;
 using Xunit;
 using ytLive.Models;
 using ytLive.ViewModels;
@@ -47,6 +48,11 @@ public sealed class RoundClipInteractionTests
         var app = new App();
         app.InitializeComponent();
 
+        // Never let the real MainWindow read/write the user's actual layout DB —
+        // Shutdown() saves the layout, which would persist these test sources
+        // over the real ones. Point it at a throwaway temp DB instead.
+        var tempDb = System.IO.Path.Combine(System.IO.Path.GetTempPath(), $"ytLlive-test-{Guid.NewGuid():N}.db");
+        MainViewModel.LayoutPathOverride = tempDb;
         var window = new MainWindow();
         var vm = (MainViewModel)window.DataContext;
         try
@@ -103,6 +109,9 @@ public sealed class RoundClipInteractionTests
         finally
         {
             window.Close();
+            MainViewModel.LayoutPathOverride = null;
+            SqliteConnection.ClearAllPools();
+            try { System.IO.File.Delete(tempDb); } catch { /* best-effort cleanup */ }
         }
     }
 

ytLive.csproj

@@ -24,6 +24,12 @@
     <Resource Include="Assets\llama-logo-icon.png"/>
   </ItemGroup>
 
+  <ItemGroup>
+    <AssemblyAttribute Include="System.Runtime.CompilerServices.InternalsVisibleTo">
+      <_Parameter1>ytLive.Tests</_Parameter1>
+    </AssemblyAttribute>
+  </ItemGroup>
+
   <ItemGroup>
     <PackageReference Include="Microsoft.Data.Sqlite" Version="8.0.10"/>
     <PackageReference Include="SQLitePCLRaw.bundle_e_sqlite3" Version="2.1.12"/>