Add unit tests for ObjectToStringConverter

Co-authored-by: Keboo <[email protected]>

Author: Copilot

tests/MaterialDesignThemes.Wpf.Tests/Converters/ObjectToStringConverterTests.cs

@@ -0,0 +1,54 @@
+using System.Globalization;
+using MaterialDesignThemes.Wpf.Converters;
+using TUnit.Core;
+using TUnit.Assertions;
+using TUnit.Assertions.Extensions;
+using System.Threading.Tasks;
+
+namespace MaterialDesignThemes.Wpf.Tests.Converters;
+
+public sealed class ObjectToStringConverterTests
+{
+    [Test]
+    public async Task Convert_StringValue_ReturnsOriginalString()
+    {
+        var converter = ObjectToStringConverter.Instance;
+        string input = "Test String";
+        
+        var result = converter.Convert(input, typeof(string), null, CultureInfo.InvariantCulture);
+        
+        await Assert.That(result).IsEqualTo(input);
+    }
+
+    [Test]
+    public async Task Convert_NullValue_ReturnsEmptyString()
+    {
+        var converter = ObjectToStringConverter.Instance;
+        
+        var result = converter.Convert(null, typeof(string), null, CultureInfo.InvariantCulture);
+        
+        await Assert.That(result).IsEqualTo(string.Empty);
+    }
+
+    [Test]
+    public async Task Convert_NonStringValue_ReturnsEmptyString()
+    {
+        var converter = ObjectToStringConverter.Instance;
+        int input = 42;
+        
+        var result = converter.Convert(input, typeof(string), null, CultureInfo.InvariantCulture);
+        
+        await Assert.That(result).IsEqualTo(string.Empty);
+    }
+
+    [Test]
+    public async Task Convert_EmptyString_ReturnsEmptyString()
+    {
+        var converter = ObjectToStringConverter.Instance;
+        string input = string.Empty;
+        
+        var result = converter.Convert(input, typeof(string), null, CultureInfo.InvariantCulture);
+        
+        await Assert.That(result).IsEqualTo(string.Empty);
+    }
+}