test: tighten byte count and file identity coverage

src/infra/json-utf8-bytes.test.ts

@@ -2,10 +2,24 @@ import { describe, expect, it } from "vitest";
 import { jsonUtf8Bytes } from "./json-utf8-bytes.js";
 
 describe("jsonUtf8Bytes", () => {
-  it("returns utf8 byte length for serializable values", () => {
-    expect(jsonUtf8Bytes({ a: "x", b: [1, 2, 3] })).toBe(
-      Buffer.byteLength(JSON.stringify({ a: "x", b: [1, 2, 3] }), "utf8"),
-    );
+  it.each([
+    {
+      name: "object payloads",
+      value: { a: "x", b: [1, 2, 3] },
+      expected: Buffer.byteLength(JSON.stringify({ a: "x", b: [1, 2, 3] }), "utf8"),
+    },
+    {
+      name: "strings",
+      value: "hello",
+      expected: Buffer.byteLength(JSON.stringify("hello"), "utf8"),
+    },
+    {
+      name: "undefined via string fallback",
+      value: undefined,
+      expected: Buffer.byteLength("undefined", "utf8"),
+    },
+  ])("returns utf8 byte length for $name", ({ value, expected }) => {
+    expect(jsonUtf8Bytes(value)).toBe(expected);
   });
 
   it("falls back to string conversion when JSON serialization throws", () => {
@@ -13,4 +27,8 @@ describe("jsonUtf8Bytes", () => {
     circular.self = circular;
     expect(jsonUtf8Bytes(circular)).toBe(Buffer.byteLength("[object Object]", "utf8"));
   });
+
+  it("uses string conversion for BigInt serialization failures", () => {
+    expect(jsonUtf8Bytes(12n)).toBe(Buffer.byteLength("12", "utf8"));
+  });
 });