How to correctly identify synchronous methods that have been modified to be asynchronous when using asynchronous decorators to decorate synchronous methods.

function AsyncDecorator() {
  return (target: any, propertyKey: string, descriptor: PropertyDescriptor) => {
    const originalMethod = descriptor.value;
    descriptor.value = async function (...args: any[]) {
      await sleep(100);
      const result = await originalMethod.apply(this, args);
      return result;
    };
    return descriptor;
  };
}

async function sleep(ms: number) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

class Test {
  // This function appears to be a synchronous function, but has been changed to an asynchronous function by an asynchronous decorator, but I didn't know that
  @AsyncDecorator()
  fun(): string {
    return 'Hello World!';
  }
}

const result = new Test().fun();
console.log(result); // Expect results: Hello World!  Actual result: Promise {<pending>}