void test_stack() {
  THStack *hs = new THStack("hs", "test");
  TH1F *h[3];
  for ( Int_t i = 0; i < 3; i++ ) {
    h[i] = new TH1F(Form("h%d", i), Form("test h%d"), 50, -5, 5);
    h[i]->FillRandom("gaus");
    h[i]->SetLineColor(2*i+2);
    hs->Add(h[i]);
  }
  hs->Draw("ehist nostack");
}