tests: add additional test coverage

tests/AnthropicClient.Tests/Unit/Models/CustomSourceTests.cs

@@ -1,7 +1,17 @@
 namespace AnthropicClient.Tests.Unit.Models;
 
-public class CustomSourceTests
+public class CustomSourceTests : SerializationTest
 {
+  private readonly string _testJson = @"{
+    ""type"": ""content"",
+    ""content"": [
+      {
+        ""type"": ""text"",
+        ""text"": ""Sample text""
+      }
+    ]
+  }";
+
   [Fact]
   public void Constructor_WhenCalled_ItShouldSetProperties()
   {
@@ -32,4 +42,30 @@ public class CustomSourceTests
 
     act.Should().Throw<ArgumentNullException>();
   }
+
+  [Fact]
+  public void JsonSerialization_WhenSerialized_ItShouldHaveExpectedShape()
+  {
+    var content = new List<TextContent>
+    {
+      new("Sample text")
+    };
+    var source = new CustomSource(content);
+
+    var result = Serialize<Source>(source);
+
+    JsonAssert.Equal(_testJson, result);
+  }
+
+  [Fact]
+  public void JsonDeserialization_WhenDeserialized_ItShouldHaveExpectedShape()
+  {
+    var source = Deserialize<Source>(_testJson);
+
+    var customSource = source.As<CustomSource>();
+    customSource!.Type.Should().Be("content");
+    customSource.Content.Should().HaveCount(1);
+    customSource.Content[0].Type.Should().Be("text");
+    customSource.Content[0].Text.Should().Be("Sample text");
+  }
 }