Improvement: add test for t8_forest_element_neighbor_eclass

src/t8_cmesh/t8_cmesh_examples.h

@@ -345,7 +345,7 @@ t8_cmesh_new_hybrid_gate (sc_MPI_Comm comm);
 t8_cmesh_t
 t8_cmesh_new_hybrid_gate_deformed (sc_MPI_Comm comm);
 
-/** Construct a full hybrig cmesh, with 1 hex, 1 pyra, 1 prism and 1 tet
+/** Construct a full hybrid cmesh, with 1 hex, 1 pyra, 1 prism and 1 tet
  * This cmesh is used for testing and debugging.
  * \param [in] comm        The MPI communicator used to commit the cmesh.
  * \return                 A committed and replicated hybrid cmesh of 4 trees.

test/CMakeLists.txt

@@ -161,6 +161,7 @@ add_t8_cpp_test( NAME t8_gtest_partition_data_parallel            SOURCES t8_for
 add_t8_cpp_test( NAME t8_gtest_set_partition_offset_parallel      SOURCES t8_forest/t8_gtest_set_partition_offset.cxx )
 add_t8_cpp_test( NAME t8_gtest_partition_for_coarsening_parallel  SOURCES t8_forest/t8_gtest_partition_for_coarsening.cxx )
 add_t8_cpp_test( NAME t8_gtest_weighted_partitioning_parallel     SOURCES t8_forest/t8_gtest_weighted_partitioning.cxx )
+add_t8_cpp_test( NAME t8_gtest_element_neighbor_eclass_parallel   SOURCES t8_forest/t8_gtest_element_neighbor_eclass.cxx )
 
 add_t8_cpp_test( NAME t8_gtest_element_is_leaf_parallel     SOURCES t8_forest/t8_gtest_element_is_leaf.cxx t8_gtest_adapt_callbacks.cxx )
 add_t8_cpp_test( NAME t8_gtest_permute_hole_serial          SOURCES t8_forest_incomplete/t8_gtest_permute_hole.cxx )

test/t8_forest/t8_gtest_element_neighbor_eclass.cxx

@@ -0,0 +1,121 @@
+/*
+  This file is part of t8code.
+  t8code is a C library to manage a collection (a forest) of multiple
+  connected adaptive space-trees of general element classes in parallel.
+
+  Copyright (C) 2026 the developers
+
+  t8code is free software; you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation; either version 2 of the License, or
+  (at your option) any later version.
+
+  t8code is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with t8code; if not, write to the Free Software Foundation, Inc.,
+  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+*/
+
+#include <gtest/gtest.h>
+
+#include <test/t8_gtest_schemes.hxx>
+
+#include <t8_forest/t8_forest_ghost.h>
+#include <t8_cmesh/t8_cmesh_examples.h>
+#include <t8_forest/t8_forest_private.h>
+
+struct element_neighbor_eclass: public testing::TestWithParam<std::tuple<int, int>>
+{
+ protected:
+  void
+  SetUp () override
+  {
+    const bool do_ghost = true;
+    const int scheme_id = std::get<0> (GetParam ());
+    scheme = create_from_scheme_id (scheme_id);
+    const int level = std::get<1> (GetParam ());
+
+    // Construct a hybrid coarse mesh
+    cmesh = t8_cmesh_new_full_hybrid (sc_MPI_COMM_WORLD);
+
+    // Build a uniform forest
+    forest = t8_forest_new_uniform (cmesh, scheme, level, do_ghost, sc_MPI_COMM_WORLD);
+  }
+
+  void
+  TearDown () override
+  {
+    t8_forest_unref (&forest);
+  }
+
+  t8_cmesh_t cmesh;
+  t8_forest_t forest;
+  const t8_scheme *scheme;
+};
+
+TEST_P (element_neighbor_eclass, test_half_neighbors)
+{
+  // Iterate over all trees (local and ghosts)
+  const t8_locidx_t num_local_trees = t8_forest_get_num_local_trees (forest);
+  const t8_locidx_t num_ghost_trees = t8_forest_get_num_ghost_trees (forest);
+
+  for (t8_locidx_t itree = 0; itree < num_local_trees + num_ghost_trees; itree++) {
+
+    const t8_eclass_t tree_eclass = t8_forest_get_tree_class (forest, itree);
+    const bool is_ghost = itree >= num_local_trees;
+    const t8_locidx_t ghost_tree_id = itree - num_local_trees;
+    const t8_element_array_t *leaf_elements = is_ghost ? t8_forest_ghost_get_tree_leaf_elements (forest, ghost_tree_id)
+                                                       : t8_forest_get_tree_leaf_element_array (forest, itree);
+    const t8_locidx_t num_leaves = t8_element_array_get_count (leaf_elements);
+    const t8_locidx_t ltreeid_in_cmesh = t8_forest_ltreeid_to_cmesh_ltreeid (forest, itree);
+
+    // Iterate over all leaf elements
+    for (t8_locidx_t ileaf = 0; ileaf < num_leaves; ++ileaf) {
+
+      const t8_element_t *element = t8_element_array_index_locidx (leaf_elements, ileaf);
+
+      // Iterate over all faces
+      for (int iface = 0; iface < scheme->element_get_num_faces (tree_eclass, element); iface++) {
+
+        // Get the eclass of the face neighbor (function to test)
+        const t8_eclass_t neigh_class = t8_forest_element_neighbor_eclass (forest, itree, element, iface);
+
+        // Inside the current tree
+        if (!scheme->element_is_root_boundary (tree_eclass, element, iface)) {
+          // We expect to get the same eclass
+          EXPECT_EQ (neigh_class, tree_eclass);
+        }
+        // Crossing a tree boundary
+        else {
+          // Get neighbor tree id
+          const int tree_face = scheme->element_get_tree_face (tree_eclass, element, iface);
+          t8_locidx_t const neighbor_id
+            = t8_cmesh_get_face_neighbor (cmesh, ltreeid_in_cmesh, tree_face, nullptr, nullptr);
+
+          if (neighbor_id < 0) {
+            // No neighbor
+            EXPECT_EQ (neigh_class, T8_ECLASS_INVALID);
+          }
+          else {
+            // Neighbor
+            const bool neighbor_is_ghost = t8_cmesh_treeid_is_ghost (cmesh, neighbor_id);
+            if (!neighbor_is_ghost) {
+              EXPECT_EQ (neigh_class, t8_cmesh_get_tree_class (cmesh, neighbor_id));
+            }
+            else {
+              const t8_locidx_t lghost_neighbor_id = neighbor_id - t8_cmesh_get_num_local_trees (cmesh);
+              EXPECT_EQ (neigh_class, t8_cmesh_get_ghost_class (cmesh, lghost_neighbor_id));
+            }
+          }
+        }
+      }
+    }
+  }
+}
+
+INSTANTIATE_TEST_SUITE_P (t8_gtest_element_neighbor_eclass, element_neighbor_eclass,
+                          testing::Combine (AllSchemeCollections, testing::Range (0, 4)));