Add tests for TBufferMerger and TBufferMergerFile

io/io/CMakeLists.txt

@@ -18,4 +18,8 @@ ROOT_LINKER_LIBRARY(${libname} $<TARGET_OBJECTS:RIOObjs> $<TARGET_OBJECTS:RootPc
                                DEPENDENCIES Core Thread)
 ROOT_INSTALL_HEADERS()
 
+if(testing)
+  add_subdirectory(test)
+endif()
+
 #--- Extra rules ----------------------------------------------------------

io/io/test/CMakeLists.txt

@@ -0,0 +1 @@
+ROOT_ADD_GTEST(testTBufferMerger TBufferMerger.cxx LIBRARIES RIO Tree)

io/io/test/TBufferMerger.cxx

@@ -0,0 +1,127 @@
+#include "ROOT/TBufferMerger.hxx"
+
+#include "TFile.h"
+#include "TROOT.h"
+#include "TTree.h"
+
+#include <memory>
+#include <thread>
+
+#include "gtest/gtest.h"
+
+using namespace ROOT::Experimental;
+
+static void Fill(std::shared_ptr<TTree> tree, int init, int count)
+{
+   int n = 0;
+
+   tree->Branch("n", &n, "n/I");
+
+   for (int i = 0; i < count; ++i) {
+      n = init + i;
+      tree->Fill();
+   }
+}
+
+TEST(TBufferMerger, CreateAndDestroy)
+{
+   TBufferMerger merger("tbuffermerger_create.root");
+}
+
+TEST(TBufferMerger, CreateAndDestroyWithAttachedFiles)
+{
+   TBufferMerger merger("tbuffermerger_create.root");
+
+   auto f1 = merger.GetFile();
+   auto f2 = merger.GetFile();
+   auto f3 = merger.GetFile();
+}
+
+TEST(TBufferMerger, SequentialTreeFill)
+{
+   int nevents = 1024;
+
+   ROOT::EnableThreadSafety();
+
+   {
+      TBufferMerger merger("tbuffermerger_sequential.root");
+
+      auto myfile = merger.GetFile();
+      auto mytree = std::make_shared<TTree>("mytree", "mytree");
+
+      Fill(mytree, 0, nevents);
+
+      mytree->Write();
+      myfile->Write();
+   }
+}
+
+TEST(TBufferMerger, ParallelTreeFill)
+{
+   int nthreads = 4;
+   int nevents = 256;
+
+   ROOT::EnableThreadSafety();
+
+   {
+      TBufferMerger merger("tbuffermerger_parallel.root");
+      std::vector<std::thread> threads;
+      for (int i = 0; i < nthreads; ++i) {
+         threads.emplace_back([=, &merger]() {
+            auto myfile = merger.GetFile();
+            auto mytree = std::make_shared<TTree>("mytree", "mytree");
+
+            Fill(mytree, i * nevents, nevents);
+
+            mytree->Write();
+            myfile->Write();
+         });
+      }
+
+      for (auto &&t : threads) t.join();
+   }
+}
+
+TEST(TBufferMerger, CheckTreeFillResults)
+{
+   int sum_s, sum_p;
+
+   { // sum of all branch values in sequential mode
+      auto f = std::unique_ptr<TFile>(TFile::Open("tbuffermerger_sequential.root"));
+      auto t = std::unique_ptr<TTree>((TTree *)f->Get("mytree"));
+
+      int n, sum = 0;
+      int nentries = (int)t->GetEntries();
+
+      t->SetBranchAddress("n", &n);
+
+      for (int i = 0; i < nentries; ++i) {
+         t->GetEntry(i);
+         sum += n;
+      }
+
+      sum_s = sum;
+   }
+
+   { // sum of all branch values in parallel mode
+      auto f = std::unique_ptr<TFile>(TFile::Open("tbuffermerger_parallel.root"));
+      auto t = std::unique_ptr<TTree>((TTree *)f->Get("mytree"));
+
+      int n, sum = 0;
+      int nentries = (int)t->GetEntries();
+
+      t->SetBranchAddress("n", &n);
+
+      for (int i = 0; i < nentries; ++i) {
+         t->GetEntry(i);
+         sum += n;
+      }
+
+      sum_p = sum;
+   }
+
+   // Note: 0 + 1 + ... + 1024 = 523776
+
+   EXPECT_EQ(523776, sum_s);
+   EXPECT_EQ(523776, sum_p);
+}