Star favourite sceneries in the list

A right click stars or unstars the scenery under it; the starred ones are
gathered in a group on top and marked where they belong. They are kept in
favorites.txt beside the settings, not in eu07.ini.

StarterNG.Tests/FavoriteSceneriesTests.cs

@@ -0,0 +1,38 @@
+using StarterNG.Application;
+using StarterNG.Domain.Sceneries;
+using StarterNG.Tests.Fakes;
+
+namespace StarterNG.Tests;
+
+public class FavoriteSceneriesTests
+{
+    private const string FavoritesPath = "/home/user/.config/MaSzyna/favorites.txt";
+
+    [Fact]
+    public void A_starred_scenery_stays_starred_after_a_restart()
+    {
+        var installation = new TestInstallation(new InMemoryFileSystem()
+            .WithLegacyFile(TestInstallation.At("scenery", "td.scn"), "//$n Testowa"));
+        var scenery = Assert.Single(installation.Sceneries.LoadAll());
+
+        new FavoriteSceneries(installation.Files, installation.Log, FavoritesPath).Toggle(scenery);
+        var restarted = new FavoriteSceneries(installation.Files, installation.Log, FavoritesPath);
+
+        Assert.True(restarted.Contains(scenery));
+        Assert.Equal("td.scn", installation.Files.ReadAllText(FavoritesPath));
+    }
+
+    [Fact]
+    public void Starring_again_unstars()
+    {
+        var installation = new TestInstallation(new InMemoryFileSystem()
+            .WithLegacyFile(TestInstallation.At("scenery", "td.scn"), "//$n Testowa"));
+        var scenery = Assert.Single(installation.Sceneries.LoadAll());
+        var favorites = new FavoriteSceneries(installation.Files, installation.Log, FavoritesPath);
+
+        favorites.Toggle(scenery);
+        favorites.Toggle(scenery);
+
+        Assert.False(favorites.Contains(scenery));
+    }
+}

StarterNG.Tests/ScenarioPresentationTests.cs

@@ -80,6 +80,36 @@ public class SceneryTreeBuilderTests
         return (new SceneryTreeBuilder(new SceneryTranslations(files, installation.Log)), sceneries);
     }
 
+    [Fact]
+    public void Starred_sceneries_are_gathered_on_top_and_starred_where_they_belong()
+    {
+        var (builder, sceneries) = Build("//$l Śląsk", "//$l Śląsk", "//$n Aaa luzem");
+        string starred = SceneryTreeBuilder.Star + sceneries.Single(scenery => scenery.Path.EndsWith("s1.scn")).DisplayName;
+        string plain = sceneries.Single(scenery => scenery.Path.EndsWith("s0.scn")).DisplayName;
+
+        var nodes = builder.Build(sceneries, includeArchival: true, "en",
+                                  scenery => scenery.Path.EndsWith("s1.scn"), "Ulubione");
+
+        var top = nodes[0];
+        Assert.True(top.IsGroup);
+        Assert.Equal(SceneryTreeBuilder.Star + "Ulubione", top.Label);
+        Assert.Equal(starred, Assert.Single(top.Children).Label);
+
+        var group = Assert.Single(nodes, node => node.Label == "Śląsk");
+        Assert.Contains(group.Children, node => node.Label == starred);
+        Assert.Contains(group.Children, node => node.Label == plain);
+    }
+
+    [Fact]
+    public void Without_favourites_there_is_no_favourites_group()
+    {
+        var (builder, sceneries) = Build("//$n Bytom");
+
+        var nodes = builder.Build(sceneries, includeArchival: true, "en", _ => false, "Ulubione");
+
+        Assert.DoesNotContain(nodes, node => node.Label.StartsWith(SceneryTreeBuilder.Star));
+    }
+
     [Fact]
     public void Scenarios_declaring_a_group_are_gathered_under_it()
     {