Rewrite TextBounds test

tests/Avalonia.Skia.UnitTests/Media/TextFormatting/TextLineTests.cs

@@ -665,14 +665,17 @@ namespace Avalonia.Skia.UnitTests.Media.TextFormatting
                 var text = "0123".AsMemory();
                 var shaperOption = new TextShaperOptions(Typeface.Default.GlyphTypeface, 10, 0, CultureInfo.CurrentCulture);
 
+                var shapedBuffer = TextShaper.Current.ShapeText(new ReadOnlySlice<char>(text), shaperOption);
+                var firstRun = new ShapedTextCharacters(shapedBuffer, defaultProperties);
+
                 var textRuns = new List<TextRun>
                 {
-                    new ShapedTextCharacters(TextShaper.Current.ShapeText(new ReadOnlySlice<char>(text), shaperOption), defaultProperties),
                     new CustomDrawableRun(),
-                    new ShapedTextCharacters(TextShaper.Current.ShapeText(new ReadOnlySlice<char>(text, text.Length + 1, text.Length), shaperOption), defaultProperties),
+                    firstRun,
                     new CustomDrawableRun(),
-                    new ShapedTextCharacters(TextShaper.Current.ShapeText(new ReadOnlySlice<char>(text, text.Length * 2 + 2, text.Length), shaperOption), defaultProperties),
+                    new ShapedTextCharacters(shapedBuffer, defaultProperties),
                     new CustomDrawableRun(),
+                    new ShapedTextCharacters(shapedBuffer, defaultProperties)
                 };
 
                 var textSource = new FixedRunsTextSource(textRuns);
@@ -687,6 +690,16 @@ namespace Avalonia.Skia.UnitTests.Media.TextFormatting
 
                 Assert.Equal(1, textBounds.Count);
                 Assert.Equal(textLine.WidthIncludingTrailingWhitespace, textBounds.Sum(x => x.Rectangle.Width));
+
+                textBounds = textLine.GetTextBounds(0, firstRun.Text.Length);
+
+                Assert.Equal(1, textBounds.Count);
+                Assert.Equal(firstRun.Size.Width, textBounds[0].Rectangle.Width);
+
+                textBounds = textLine.GetTextBounds(0, firstRun.Text.Length + 1);
+
+                Assert.Equal(1, textBounds.Count);
+                Assert.Equal(firstRun.Size.Width + 14, textBounds[0].Rectangle.Width);
             }
         }