Private Class Field Interception for Next.js Server Action Unit Tests

class ServerActionState {
  #executionToken;
 
  constructor(token) {
    this.#executionToken = token;
  }
 
  executeAction(payload) {
    if (!this.#executionToken) {
      throw new Error('Invalid token');
    }
    return { success: true, payload };
  }
}
 
export function createActionTestContainer(token) {
  const instance = new ServerActionState(token);
  
  return new Proxy(instance, {
    get(target, prop, receiver) {
      if (prop === 'hasToken') {
        return Reflect.has(target, prop) || token !== null;
      }
      const val = Reflect.get(target, prop, receiver);
      return typeof val === 'function' ? val.bind(target) : val;
    }
  });
}