Temporarily make half the thumbnails act as missing

StarterNG.Tests/MiniTextureIndexTests.cs

@@ -12,7 +12,7 @@ public class MiniTextureIndexTests
         "406r", "424z", "621z", "z1kd", "gags", "eaos", "falns", "uacs", "sgs", "kbs"
     };
 
-    private static MiniTextureIndex Build(int missRate)
+    private static MiniTextureIndex Build(int? missRate)
     {
         var files = new InMemoryFileSystem();
         foreach (string name in Names)
@@ -20,14 +20,14 @@ public class MiniTextureIndexTests
         files.WithFile(TestInstallation.At("textures", "mini", "other.bmp"), "bitmap");
 
         var environment = new FakeEnvironment();
-        if (missRate > 0)
-            environment.With(MiniTextureIndex.MissRateVariable, missRate.ToString());
+        if (missRate is { } rate)
+            environment.With(MiniTextureIndex.MissRateVariable, rate.ToString());
 
         return new MiniTextureIndex(files, new GamePaths(TestInstallation.Root), environment);
     }
 
     [Fact]
-    public void Without_the_debug_variable_every_thumbnail_loads()
+    public void Setting_the_variable_to_zero_shows_the_installation_as_it_is()
     {
         var index = Build(missRate: 0);
 
@@ -35,6 +35,18 @@ public class MiniTextureIndexTests
         Assert.All(Names, name => Assert.True(index.Has(name)));
     }
 
+    [Fact]
+    public void The_temporary_default_still_hides_half_the_thumbnails()
+    {
+        // Guards the testing default in MiniTextureIndex.DefaultMissRate. When
+        // that goes back to 0 for release, this test is what says so - change it
+        // together with the constant, do not delete it quietly.
+        var index = Build(missRate: null);
+
+        Assert.Equal(50, index.SimulatedMissRate);
+        Assert.Contains(Names, name => !index.Has(name));
+    }
+
     [Fact]
     public void The_debug_variable_hides_roughly_the_share_it_names()
     {

StarterNG/Infrastructure/Vehicles/MiniTextureIndex.cs

@@ -20,14 +20,24 @@ public sealed class MiniTextureIndex : IMiniTextureIndex
     private const string FallbackName = "other";
 
     /// <summary>
-    /// Set to 1-100 to make that percentage of thumbnails behave as if the
-    /// installation did not have their file - the vehicle then falls back to
-    /// other.bmp exactly as one naming an unknown thumbnail would. For checking
-    /// how a consist looks when some of its stock has no picture of its own.
-    /// Off unless the variable is set.
+    /// Set to 0-100 to override <see cref="DefaultMissRate"/>: the percentage of
+    /// thumbnails that behave as if the installation did not have their file, so
+    /// the vehicle falls back to other.bmp exactly as one naming an unknown
+    /// thumbnail would. Set it to 0 to see the installation as it really is.
     /// </summary>
     public const string MissRateVariable = "STARTER_DEBUG_MISSING_MINI";
 
+    /// <summary>
+    /// TEMPORARY, FOR TESTING THE MISSING-THUMBNAIL DRAWING. Half the vehicles in
+    /// every consist will show the other.bmp stand-in instead of their own
+    /// picture, whether or not the installation is complete.
+    ///
+    /// Set this back to 0 before release - it is the whole of the switch, and
+    /// MiniTextureIndexTests.The_temporary_default_still_hides_half_the_thumbnails
+    /// fails the moment it changes, so nothing ships it by accident.
+    /// </summary>
+    private const int DefaultMissRate = 50;
+
     private readonly IFileSystem _files;
     private readonly IGamePaths _paths;
     private readonly int _missRate;
@@ -93,7 +103,7 @@ public sealed class MiniTextureIndex : IMiniTextureIndex
         string? raw = environment?.GetVariable(MissRateVariable);
         return int.TryParse(raw, NumberStyles.Integer, CultureInfo.InvariantCulture, out int rate)
             ? Math.Clamp(rate, 0, 100)
-            : 0;
+            : DefaultMissRate;
     }
 
     private Dictionary<string, string> Index()