Add test coverage for messageSizeWithinLimit utility function

[Copilot]

The messageSizeWithinLimit utility function lacked test coverage for various message types and edge cases, particularly Unicode characters and nested objects.

Changes

• tests/utils.spec.ts: Added 18 test cases covering basic types, Unicode/multi-byte characters, nested structures, boundary conditions, and edge cases
• jest.setup.js: Polyfills TextEncoder/TextDecoder for jsdom environment (not available by default)
• package.json: Configured Jest to load setup file
• eslint.config.mjs: Added Node.js globals for Jest setup file

Test Coverage

// Validates accurate UTF-8 byte counting
test("handles Unicode characters correctly", () => {
  const message = "🎉";  // 4-byte UTF-8 emoji
  const size = new TextEncoder().encode(JSON.stringify(message)).length;
  expect(messageSizeWithinLimit(message, size)).toBe(true);
  expect(messageSizeWithinLimit(message, size - 1)).toBe(false);
});

// Validates nested object serialization size
test("handles nested objects", () => {
  const message = { outer: { inner: { deep: "value" } } };
  const size = new TextEncoder().encode(JSON.stringify(message)).length;
  expect(messageSizeWithinLimit(message, size)).toBe(true);
});

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.