void EffiFitTest() {
  TEfficiency* pEff = new TEfficiency("eff","my efficiency;x;#epsilon",20,0,10);
  TRandom3 rand3;
  bool bPassed;
  double x;
  for(int i=0; i<10000; ++i)
  {
    //simulate events with variable under investigation
    x = rand3.Uniform(10);
    //check selection: bPassed = DoesEventPassSelection(x)
    bPassed = rand3.Rndm() < TMath::Gaus(x,5,4);
    pEff->Fill(bPassed,x);
  }
  //create a function for fitting and do the fit
  TF1* f1 = new TF1("f1","gaus",0,10);
  f1->SetParameters(1,5,2);
  TFitResultPtr res = pEff->Fit(f1, "V S");
  //!!!!!!! show that the returned fit result pointer is nullptr !!!!!!!!
  cout << res.Get() << endl;
  //!!!!!!! cause a crash !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
  (res.Get())->Print();
  //create a threshold function
  TF1* f2 = new TF1("thres","0.8",0,10);
  f2->SetLineColor(kRed);
  //add it to the list of functions
  //use add first because the parameters of the last function will be displayed
  pEff->GetListOfFunctions()->AddFirst(f2);
  pEff->Draw("AP");
}