Move converter, implement serialize, and add roundtrip test

Author: DavidBoike

src/Octokit.Webhooks/Models/ProjectsV2ItemEvent/ChangesFieldValueChangeConverter.cs renamed to src/Octokit.Webhooks/Converter/ChangesFieldValueChangeConverter.cs

@@ -28,5 +28,30 @@ public class ChangesFieldValueChangeConverter : JsonConverter<ChangesFieldValueC
         }
     }
 
-    public override void Write(Utf8JsonWriter writer, ChangesFieldValueChangeBase value, JsonSerializerOptions options) => throw new NotImplementedException();
+    public override void Write(Utf8JsonWriter writer, ChangesFieldValueChangeBase value, JsonSerializerOptions options)
+    {
+        if (value is ChangesFieldValueScalarChange scalarChange)
+        {
+            if (scalarChange.StringValue is not null)
+            {
+                writer.WriteStringValue(scalarChange.StringValue);
+            }
+            else if (scalarChange.NumericValue is not null)
+            {
+                writer.WriteNumberValue(scalarChange.NumericValue.Value);
+            }
+            else
+            {
+                writer.WriteNullValue();
+            }
+        }
+        else if (value is ChangesFieldValueChange change)
+        {
+            JsonSerializer.Serialize(writer, change, options);
+        }
+        else
+        {
+            writer.WriteNullValue();
+        }
+    }
 }

test/Octokit.Webhooks.Test/Converter/ChangesFieldValueChangeConverterTests.cs

@@ -0,0 +1,72 @@
+namespace Octokit.Webhooks.Test.Converter;
+
+using System;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using AwesomeAssertions;
+using Octokit.Webhooks.Models.ProjectsV2ItemEvent;
+using Xunit;
+
+public class ChangesFieldValueChangeConverterTests(ITestOutputHelper output)
+{
+    private readonly JsonSerializerOptions options = new()
+    {
+        WriteIndented = true,
+        Converters =
+        {
+            new ChangesFieldValueChangeConverter(),
+        },
+    };
+
+    [Fact]
+    public void Roundtrip()
+    {
+        var test = new TestObject
+        {
+            AsString = new ChangesFieldValueScalarChange { StringValue = "Hello world" },
+            AsNumber = new ChangesFieldValueScalarChange { NumericValue = 3.1415926m },
+            AsObject = new ChangesFieldValueChange
+            {
+                Color = "color",
+                Description = "description",
+                Id = "12345",
+                Name = "Name",
+            },
+        };
+
+        var serialized = JsonSerializer.Serialize(test, this.options);
+        output.WriteLine(serialized);
+
+        var deserialized = JsonSerializer.Deserialize<TestObject>(serialized, this.options);
+
+        deserialized.Should().NotBeNull();
+        deserialized.AsString.Should().NotBeNull().And.BeOfType<ChangesFieldValueScalarChange>();
+        deserialized.AsNumber.Should().NotBeNull().And.BeOfType<ChangesFieldValueScalarChange>();
+
+        (deserialized.AsString as ChangesFieldValueScalarChange)?.StringValue.Should().Be("Hello world");
+        (deserialized.AsString as ChangesFieldValueScalarChange)?.NumericValue.Should().BeNull();
+
+        (deserialized.AsNumber as ChangesFieldValueScalarChange)?.StringValue.Should().BeNull();
+        (deserialized.AsNumber as ChangesFieldValueScalarChange)?.NumericValue.Should().Be(3.1415926m);
+
+        deserialized.AsObject.Should().NotBeNull().And.BeOfType<ChangesFieldValueChange>();
+        var changeObject = deserialized.AsObject.As<ChangesFieldValueChange>();
+
+        changeObject.Color.Should().Be("color");
+        changeObject.Description.Should().Be("description");
+        changeObject.Id.Should().Be("12345");
+        changeObject.Name.Should().Be("Name");
+    }
+
+    internal sealed class TestObject
+    {
+        [JsonPropertyName("as_string")]
+        public ChangesFieldValueChangeBase AsString { get; init; } = null!;
+
+        [JsonPropertyName("as_number")]
+        public ChangesFieldValueChangeBase AsNumber { get; init; } = null!;
+
+        [JsonPropertyName("as_object")]
+        public ChangesFieldValueChangeBase AsObject { get; init; } = null!;
+    }
+}