diff --git a/src/handlers/tsonCircular.test.ts b/src/handlers/tsonCircular.test.ts
new file mode 100644
index 00000000..a1a31be0
--- /dev/null
+++ b/src/handlers/tsonCircular.test.ts
@@ -0,0 +1,50 @@
+/* eslint-disable eslint-comments/disable-enable-pair */
+/* eslint-disable @typescript-eslint/no-unsafe-member-access */
+/* eslint-disable @typescript-eslint/no-explicit-any */
+import { expect, test } from "vitest";
+
+import { createTson } from "../tson.js";
+import { tsonCircular } from "./index.js";
+
+test("circular", () => {
+	const t = createTson({
+		types: [tsonCircular],
+	});
+
+	{
+		const expected: any = {};
+
+		expected.a = expected;
+
+		expect(t.serialize(expected).json).toBe({
+			a: [
+				//
+				"Circular",
+				0, // <-- 0 means that the direct parent is circular target
+				"__tson",
+			],
+		});
+
+		// const deserialized = t.parse(stringified);
+		// expect(deserialized).toEqual(expected);
+	}
+
+	{
+		const expected: any = {
+			a: {
+				b: {},
+			},
+		};
+
+		expected.a.b.a = expected;
+
+		expect(t.serialize(expected).json).toBe({
+			a: [
+				//
+				"Circular",
+				1, // <-- 1 means that the grandparent is circular target
+				"__tson",
+			],
+		});
+	}
+});