random_refactor.cpp

class CSGObject 
{
   public:
      void CSGObject::init()
      {
         m_rng = std::unique_ptr<CRandom>(new CRandom(m_seed));
      }
      static void set_global_seed(uint32_t seed) 
      {
        CSGObject::m_seed = seed;
      }
 
      static uint32_t get_global_seed()
      {
        uint32_t seed = CSGObject::m_seed;
        return seed;
      }
   private:
      static uint32_t m_seed;
}

uint32_t CSGObject::m_seed = CRandom::generate_seed();

class subclassOfSGObject:public CSGObject
{
  void dosomething()
  {
    ...
    m_rng->random();
    ...
  }
  
  static void dosomething()
  {
    ...
    auto m_rng = std::unique_ptr<CRandom>(new CRandom(CSGObject::get_global_seed()));
    m_rng->random();
    ...
  }
}

//in the test

TEST(dosomething, random)
{
  CSGObject::set_global_seed(12345)
  ......
}