diff --git a/tests/AnthropicClient.Tests/Unit/Models/FileSourceTests.cs b/tests/AnthropicClient.Tests/Unit/Models/FileSourceTests.cs
index 6a99d28..621b585 100644
--- a/tests/AnthropicClient.Tests/Unit/Models/FileSourceTests.cs
+++ b/tests/AnthropicClient.Tests/Unit/Models/FileSourceTests.cs
@@ -32,6 +32,17 @@ public class FileSourceTests : SerializationTest
     result.Type.Should().Be(type);
   }
 
+  [Fact]
+  public void Constructor_WhenCalledWithId_ItShouldInitializeProperties()
+  {
+    var id = "id";
+
+    var result = new FileSource(id);
+
+    result.Id.Should().Be(id);
+    result.Type.Should().Be("file");
+  }
+
   [Fact]
   public void JsonSerialization_WhenSerialized_ItShouldHaveExpectedShape()
   {