Fix test

Author: ercolessi

MC/config/PWGLF/ini/tests/GeneratorLF_Coalescence_pp536TeV.C

@@ -1 +1,28 @@
-GeneratorLF_Coalescence.C
+int External()
+{
+    std::string path{"o2sim_Kine.root"};
+
+    TFile file(path.c_str(), "READ");
+    if (file.IsZombie())
+    {
+        std::cerr << "Cannot open ROOT file " << path << "\n";
+        return 1;
+    }
+
+    auto tree = (TTree *)file.Get("o2sim");
+    if (!tree)
+    {
+        std::cerr << "Cannot find tree o2sim in file " << path << "\n";
+        return 1;
+    }
+    std::vector<o2::MCTrack> *tracks{};
+    tree->SetBranchAddress("MCTrack", &tracks);
+
+    auto nEvents = tree->GetEntries();
+    if (nEvents < 1)
+    {
+        std::cerr << "No events actually generated: not OK!";
+        return 1;
+    }
+    return 0;
+}