Draw a stand-in for a missing thumbnail, pass the language code to eu07.ini

The file was getting "pl" or "en" whatever the user picked, so a simulator with
its own language file started in English.

StarterNG.Tests/MiniTextureIndexTests.cs

@@ -0,0 +1,76 @@
+using StarterNG.Infrastructure.Adapters;
+using StarterNG.Infrastructure.Vehicles;
+using StarterNG.Tests.Fakes;
+
+namespace StarterNG.Tests;
+
+public class MiniTextureIndexTests
+{
+    private static readonly string[] Names =
+    {
+        "ep07", "et22", "111a", "112a", "203v", "401k", "en57", "sm42", "st44", "412w",
+        "406r", "424z", "621z", "z1kd", "gags", "eaos", "falns", "uacs", "sgs", "kbs"
+    };
+
+    private static MiniTextureIndex Build(int missRate)
+    {
+        var files = new InMemoryFileSystem();
+        foreach (string name in Names)
+            files.WithFile(TestInstallation.At("textures", "mini", name + ".bmp"), "bitmap");
+        files.WithFile(TestInstallation.At("textures", "mini", "other.bmp"), "bitmap");
+
+        var environment = new FakeEnvironment();
+        if (missRate > 0)
+            environment.With(MiniTextureIndex.MissRateVariable, missRate.ToString());
+
+        return new MiniTextureIndex(files, new GamePaths(TestInstallation.Root), environment);
+    }
+
+    [Fact]
+    public void Without_the_debug_variable_every_thumbnail_loads()
+    {
+        var index = Build(missRate: 0);
+
+        Assert.Equal(0, index.SimulatedMissRate);
+        Assert.All(Names, name => Assert.True(index.Has(name)));
+    }
+
+    [Fact]
+    public void The_debug_variable_hides_roughly_the_share_it_names()
+    {
+        var index = Build(missRate: 50);
+
+        int hidden = Names.Count(name => !index.Has(name));
+
+        // Twenty names is a small sample, so this only asserts that the switch
+        // bites and does not take everything with it.
+        Assert.InRange(hidden, 3, Names.Length - 3);
+    }
+
+    [Fact]
+    public void A_hidden_thumbnail_stays_hidden_rather_than_flickering()
+    {
+        var index = Build(missRate: 50);
+        string hidden = Names.First(name => !index.Has(name));
+
+        for (int i = 0; i < 20; i++)
+            Assert.False(index.Has(hidden));
+    }
+
+    [Fact]
+    public void A_hidden_thumbnail_falls_back_to_other_bmp_like_an_unknown_one()
+    {
+        var index = Build(missRate: 50);
+        string hidden = Names.First(name => !index.Has(name));
+
+        Assert.EndsWith("other.bmp", index.PathFor(hidden));
+    }
+
+    [Fact]
+    public void An_unknown_name_still_falls_back_to_other_bmp_in_a_normal_run()
+    {
+        var index = Build(missRate: 0);
+
+        Assert.EndsWith("other.bmp", index.PathFor("nie-ma-takiej"));
+    }
+}

StarterNG.Tests/SettingsStoreTests.cs

@@ -26,11 +26,50 @@ public class SettingsStoreTests
         Assert.Equal(1920, settings.Width);
         Assert.Equal(1080, settings.Height);
         Assert.True(settings.Fullscreen);
-        Assert.Equal("Polski", settings.Language);
+        Assert.Equal("pl", settings.LanguageCode);
         Assert.True(settings.LanguageWasSet);
         Assert.Equal(UserIni, installation.SettingsStore.LoadedFrom);
     }
 
+    [Fact]
+    public void A_language_the_starter_does_not_ship_survives_a_round_trip()
+    {
+        // A user-supplied translation must reach the simulator as written; folding
+        // every unknown code into "en" is what forced eu07.exe into English.
+        var installation = WithHome(new InMemoryFileSystem().WithFile(UserIni, "lang zh\n"));
+        installation.SettingsStore.Load();
+
+        Assert.Equal("zh", installation.SettingsStore.Settings.LanguageCode);
+
+        installation.SettingsStore.Save();
+
+        Assert.Contains("lang zh", installation.Files.ReadAllText(UserIni));
+    }
+
+    [Fact]
+    public void A_language_chosen_in_the_picker_is_written_as_its_own_code()
+    {
+        var installation = WithHome();
+        installation.SettingsStore.Load();
+        installation.SettingsStore.Settings.Language = "中文";
+        installation.SettingsStore.Settings.LanguageCode = "zh";
+
+        installation.SettingsStore.Save();
+
+        Assert.Contains("lang zh", installation.Files.ReadAllText(UserIni));
+    }
+
+    [Fact]
+    public void With_no_language_recorded_the_file_still_names_one()
+    {
+        var installation = WithHome();
+        installation.SettingsStore.Load();
+
+        installation.SettingsStore.Save();
+
+        Assert.Contains("lang en", installation.Files.ReadAllText(UserIni));
+    }
+
     [Fact]
     public void A_first_run_falls_back_to_the_ini_shipped_with_the_installation()
     {