Fix mock font manager and add typeface collection tests

tests/Avalonia.Skia.UnitTests/Media/CustomFontManagerImpl.cs

@@ -48,7 +48,7 @@ namespace Avalonia.Skia.UnitTests.Media
                     continue;
                 }
 
-                typeface = new Typeface(customTypeface.FontFamily.Name, fontStyle, fontWeight);
+                typeface = new Typeface(customTypeface.FontFamily, fontStyle, fontWeight);
 
                 return true;
             }
@@ -83,7 +83,7 @@ namespace Avalonia.Skia.UnitTests.Media
                 case "Noto Mono":
                     {
                         var typefaceCollection = SKTypefaceCollectionCache.GetOrAddTypefaceCollection(_defaultTypeface.FontFamily);
-                        skTypeface = typefaceCollection.Get(typeface);
+                        skTypeface = typefaceCollection.Get(_defaultTypeface);
                         break;
                     }
                 default:

tests/Avalonia.Skia.UnitTests/Media/SKTypefaceCollectionCacheTests.cs

@@ -7,25 +7,33 @@ namespace Avalonia.Skia.UnitTests.Media
     public class SKTypefaceCollectionCacheTests
     {
         [Fact]
-        public void Should_Load_Typefaces_From_Invalid_Name()
+        public void Should_Get_Near_Matching_Typeface()
         {
             using (UnitTestApplication.Start(TestServices.MockPlatformRenderInterface))
             {
                 var notoMono =
                     new FontFamily("resm:Avalonia.Skia.UnitTests.Assets?assembly=Avalonia.Skia.UnitTests#Noto Mono");
 
-                var colorEmoji =
-                    new FontFamily("resm:Avalonia.Skia.UnitTests.Assets?assembly=Avalonia.Skia.UnitTests#Twitter Color Emoji");
-
                 var notoMonoCollection = SKTypefaceCollectionCache.GetOrAddTypefaceCollection(notoMono);
 
-                var typeface = new Typeface("ABC", FontStyle.Italic, FontWeight.Bold);
-
-                Assert.Equal("Noto Mono", notoMonoCollection.Get(typeface).FamilyName);
-
-                var notoColorEmojiCollection = SKTypefaceCollectionCache.GetOrAddTypefaceCollection(colorEmoji);
+                Assert.Equal("Noto Mono",
+                    notoMonoCollection.Get(new Typeface(notoMono, weight: FontWeight.Bold)).FamilyName);
+            }
+        }
+        
+        [Fact]
+        public void Should_Get_Null_For_Invalid_FamilyName()
+        {
+            using (UnitTestApplication.Start(TestServices.MockPlatformRenderInterface))
+            {
+                var notoMono =
+                    new FontFamily("resm:Avalonia.Skia.UnitTests.Assets?assembly=Avalonia.Skia.UnitTests#Noto Mono");
+                
+                var notoMonoCollection = SKTypefaceCollectionCache.GetOrAddTypefaceCollection(notoMono);
 
-                Assert.Equal("Twitter Color Emoji", notoColorEmojiCollection.Get(typeface).FamilyName);
+                var typeface = notoMonoCollection.Get(new Typeface("ABC"));
+                
+                Assert.Null(typeface);
             }
         }
     }