Guard tolerant enum converter creation

Author: niemyjski

src/Geocoding.Core/Serialization/TolerantStringEnumConverter.cs

@@ -23,7 +23,12 @@ public override JsonConverter CreateConverter(Type typeToConvert, JsonSerializer
         var converterType = nullableEnumType is null
             ? typeof(TolerantStringEnumConverter<>).MakeGenericType(typeToConvert)
             : typeof(NullableTolerantStringEnumConverter<>).MakeGenericType(nullableEnumType);
-        return (JsonConverter)Activator.CreateInstance(converterType);
+
+        var converter = Activator.CreateInstance(converterType);
+        if (converter is not JsonConverter jsonConverter)
+            throw new InvalidOperationException($"Unable to create converter '{converterType}' for enum type '{typeToConvert}'.");
+
+        return jsonConverter;
     }
 }
 

test/Geocoding.Tests/Serialization/TolerantStringEnumConverterTest.cs

@@ -1,10 +1,33 @@
 using Geocoding.Extensions;
+using System.Text.Json.Serialization;
 using Xunit;
 
 namespace Geocoding.Tests.Serialization;
 
 public class TolerantStringEnumConverterTest
 {
+    [Fact]
+    public void CreateConverter_ForEnumType_ReturnsTypedConverter()
+    {
+        // Act
+        var converter = JsonExtensions.JsonOptions.GetConverter(typeof(EnumWithUnknown));
+
+        // Assert
+        Assert.NotNull(converter);
+        Assert.IsAssignableFrom<JsonConverter<EnumWithUnknown>>(converter);
+    }
+
+    [Fact]
+    public void CreateConverter_ForNullableEnumType_ReturnsTypedConverter()
+    {
+        // Act
+        var converter = JsonExtensions.JsonOptions.GetConverter(typeof(EnumWithUnknown?));
+
+        // Assert
+        Assert.NotNull(converter);
+        Assert.IsAssignableFrom<JsonConverter<EnumWithUnknown?>>(converter);
+    }
+
     [Fact]
     public void FromJson_UnknownStringForEnumWithUnknownMember_ReturnsUnknown()
     {