adds a strings test

OpenUtau.Test/App/AppTest.cs

@@ -1,11 +1,39 @@
 using Xunit;
+using Avalonia;
+using Avalonia.Headless;
+using Avalonia.Styling;
+using OpenUtau.App;
+
+[assembly: AvaloniaTestApplication(typeof(TestAppBuilder))]
+
+public class TestAppBuilder {
+    public static AppBuilder BuildAvaloniaApp() => AppBuilder.Configure<App>()
+        .UseHeadless(new AvaloniaHeadlessPlatformOptions());
+}
 
 namespace OpenUtau.App {
     public class AppTest {
         [Fact]
         public void BuildTest() {
-            Assert.False(typeof(OpenUtau.App.App).IsAbstract);
-            Assert.False(typeof(OpenUtau.App.Program).IsAbstract);
+            Assert.False(typeof(App).IsAbstract);
+            Assert.False(typeof(Program).IsAbstract);
+        }
+
+        [Fact]
+        public void StringsTest() {
+            var appBuilder = TestAppBuilder.BuildAvaloniaApp()
+                .SetupWithoutStarting();
+            var app = appBuilder.Instance as App;
+            Assert.NotNull(app);
+
+            var languages = App.GetLanguages();
+            Assert.True(languages.Count > 1);
+            Assert.Contains("en-US", languages.Keys);
+            Assert.Contains("zh-CN", languages.Keys);
+            Assert.Contains("ja-JP", languages.Keys);
+            foreach (var pair in languages) {
+                Assert.NotNull(pair.Value);
+            }
         }
     }
 }

OpenUtau.Test/OpenUtau.Test.csproj

@@ -11,6 +11,7 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <PackageReference Include="Avalonia.Headless.XUnit" Version="11.0.4" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.9.0" />
     <PackageReference Include="Newtonsoft.Json" Version="13.0.3" />
     <PackageReference Include="System.Text.Encoding.CodePages" Version="7.0.0" />