message: Separate mpi and non-mpi Open
diff: @@ -1706,8 +1706,12 @@ TEST_F(BPWriteReadLocalVariables, ADIOS2BPWriteReadLocal1DSubFile)
  // requires using MPI_COMM_SELF so metadata won't be shared when reading
  // each subfile independently
  +#ifdef ADIOS2_HAVE_MPI
  adios2::Engine bpReader =
  io.Open(subFileName, adios2::Mode::Read, MPI_COMM_SELF);
  +#else
  + adios2::Engine bpReader = io.Open(subFileName, adios2::Mode::Read);
  +#endif
  auto var_i32 = io.InquireVariable<int32_t>("i32");
  EXPECT_EQ(var_i32.ShapeID(), adios2::ShapeID::LocalArray);
  