message: fix BP3 specific test for reading each subfile alone to make sure it is actually generating the subfiles
diff: @@ -1753,8 +1753,10 @@ TEST_F(BPWriteReadLocalVariables, ADIOS2BPWriteReadLocal1DSubFile)
  const std::string fname("BPWriteReadLocal1DSubFile.bp");
  int mpiRank = 0;
  + int mpiSize = 1;
  #if ADIOS2_USE_MPI
  MPI_Comm_rank(MPI_COMM_WORLD, &mpiRank);
  + MPI_Comm_size(MPI_COMM_WORLD, &mpiSize);
  #endif
  const size_t Nx0 = 3 + static_cast<size_t>(mpiRank);
  @@ -1770,6 +1772,12 @@ TEST_F(BPWriteReadLocalVariables, ADIOS2BPWriteReadLocal1DSubFile)
  std::iota(data[0].begin(), data[0].end(), startBlock0);
  std::iota(data[1].begin(), data[1].end(), startBlock1);
  + /* This is a test for only BP3 */
  + if (engineName != "BP3")
  + {
  + return;
  + }
  +
  #if ADIOS2_USE_MPI
  adios2::ADIOS adios(MPI_COMM_WORLD);
  #else
  @@ -1778,6 +1786,7 @@ TEST_F(BPWriteReadLocalVariables, ADIOS2BPWriteReadLocal1DSubFile)
  {
  adios2::IO io = adios.DeclareIO("TestIO");
  io.SetEngine("BP3");
  + io.SetParameter("AggregatorRatio", "1");
  const adios2::Dims shape{};
  const adios2::Dims start{};
  const adios2::Dims count{Nx0};
  