Fix bug in interval refinement test (#3331)

* Rename interval refinement test file

Pytest discovery previously ignored the interval test case, since it did not match the expected `test_` naming scheme

* Fix: implicit ghost_mode of interval mesh made explicit

* Fix: Bug for parallel interval refinement

Caused by assumption that ghost cells are refined on the process as well, which is not the case -> job of remote process that owns it

cpp/dolfinx/mesh/generation.h

@@ -200,15 +200,16 @@ Mesh<T> create_rectangle(MPI_Comm comm, std::array<std::array<double, 2>, 2> p,
 /// @param[in] comm MPI communicator to build the mesh on.
 /// @param[in] n Number of cells.
 /// @param[in] p End points of the interval.
+/// @param[in] ghost_mode ghost mode of the created mesh, defaults to none
 /// @param[in] partitioner Partitioning function for distributing cells
 /// across MPI ranks.
 /// @return A mesh.
 template <std::floating_point T = double>
-Mesh<T> create_interval(MPI_Comm comm, std::int64_t n, std::array<double, 2> p,
+Mesh<T> create_interval(MPI_Comm comm, std::int64_t n, std::array<double, 2> p, mesh::GhostMode ghost_mode = mesh::GhostMode::none,
                         CellPartitionFunction partitioner = nullptr)
 {
   if (!partitioner and dolfinx::MPI::size(comm) > 1)
-    partitioner = create_cell_partitioner();
+    partitioner = create_cell_partitioner(ghost_mode);
 
   fem::CoordinateElement<T> element(CellType::interval, 1);
   std::vector<T> x;

cpp/dolfinx/refinement/interval.h

@@ -122,7 +122,6 @@ compute_interval_refinement(const mesh::Mesh<T>& mesh,
 
   // Build the topology on the new vertices
   const auto refined_cell_count = mesh.topology()->index_map(1)->size_local()
-                                  + mesh.topology()->index_map(1)->num_ghosts()
                                   + number_of_refined_cells;
 
   std::vector<std::int64_t> cell_topology;

python/dolfinx/wrappers/mesh.cpp

@@ -246,7 +246,7 @@ void declare_mesh(nb::module_& m, std::string type)
          const PythonCellPartitionFunction& part)
       {
         return dolfinx::mesh::create_interval<T>(
-            comm.get(), n, p, create_cell_partitioner_cpp(part));
+            comm.get(), n, p, ghost_mode, create_cell_partitioner_cpp(part));
       },
       nb::arg("comm"), nb::arg("n"), nb::arg("p"), nb::arg("ghost_mode"),
       nb::arg("partitioner").none());