Quit test drivers through ApplicationExit and free test resources

Adds tests for freeing the temporary ext_resource sub-scene instance; the
animated foreground tests dispose their frame textures.

tests/ExtResourcePropertyResolverTests.cs

@@ -0,0 +1,52 @@
+namespace Cthangover.Mods.Dialog.Tests
+{
+    using Cthangover.Core.Mods.Testing;
+    using Cthangover.Core.Scenes.TscnBuild;
+    using Cthangover.Core.Scenes.TscnBuild.PropertyResolvers;
+    using Cthangover.Core.Scenes.TscnParsing;
+    using Cthangover.Mods.Interface.View;
+    using Godot;
+
+    /// <summary>Packing a nested prefab must release the temporary tree while preserving its children in the packed result.</summary>
+    public class ExtResourcePropertyResolverTests
+    {
+        private static Node temporary;
+
+        [ModTest("prefabs/packing_releases_the_temporary_tree")]
+        static void PackingReleasesTemporaryTree(ModTestContext ctx)
+        {
+            var target = new DialogBox();
+            try
+            {
+                var scene = new ParsedScene();
+                scene.ExtResources.Add(new ExtResourceRef { Id = "nested", Type = "PackedScene", Path = "test_nested.tscn" });
+                var context = new PropertyContext(scene, CreateTemporary, null);
+                new ExtResourcePropertyResolver().Apply(target, "answerBoxScene", TscnPropertyValue.FromExtResource("nested"), context);
+                ModAssert.False(GodotObject.IsInstanceValid(temporary), "packing frees its input instance immediately");
+                using var packed = target.Get("answerBoxScene").AsGodotObject() as PackedScene;
+                ModAssert.NotNull(packed, "the target retains the packed prefab");
+                var instance = packed.Instantiate();
+                try
+                {
+                    ModAssert.Equal("PackedRoot", instance.Name.ToString(), "packed root survives freeing the temporary tree");
+                    ModAssert.Equal(1, instance.GetChildCount(), "packed child is retained");
+                    ModAssert.Equal("PackedChild", instance.GetChild(0).Name.ToString(), "child owners were assigned before packing");
+                }
+                finally { instance.Free(); }
+            }
+            finally
+            {
+                target.Free();
+                if (GodotObject.IsInstanceValid(temporary)) temporary.Free();
+                temporary = null;
+            }
+        }
+
+        private static Node CreateTemporary(string path)
+        {
+            temporary = new Control { Name = "PackedRoot" };
+            temporary.AddChild(new Label { Name = "PackedChild", Text = "nested prefab" });
+            return temporary;
+        }
+    }
+}