From 04ef4844c5eceaf41e07c52242faec2f9fbe8bf4 Mon Sep 17 00:00:00 2001
From: Jean-Paul Pelteret <jppelteret@gmail.com>
Date: Wed, 5 Jan 2022 19:25:04 +0100
Subject: [PATCH] Add test for filtered iterators and FEInterfaceValues

---
 tests/grid/filtered_iterator_08.cc     | 106 +++++++++++++++++++++++++
 tests/grid/filtered_iterator_08.output |   2 +
 2 files changed, 108 insertions(+)
 create mode 100644 tests/grid/filtered_iterator_08.cc
 create mode 100644 tests/grid/filtered_iterator_08.output

diff --git a/tests/grid/filtered_iterator_08.cc b/tests/grid/filtered_iterator_08.cc
new file mode 100644
index 0000000000..b9e3ea00c3
--- /dev/null
+++ b/tests/grid/filtered_iterator_08.cc
@@ -0,0 +1,106 @@
+// ---------------------------------------------------------------------
+//
+// Copyright (C) 2021 by the deal.II authors
+//
+// This file is part of the deal.II library.
+//
+// The deal.II library is free software; you can use it, redistribute
+// it, and/or modify it under the terms of the GNU Lesser General
+// Public License as published by the Free Software Foundation; either
+// version 2.1 of the License, or (at your option) any later version.
+// The full text of the license can be found in the file LICENSE.md at
+// the top level directory of deal.II.
+//
+// ---------------------------------------------------------------------
+
+// Check that filtered iterators can be used with using FEInterfaceValues.
+
+#include <deal.II/base/quadrature_lib.h>
+
+#include <deal.II/dofs/dof_handler.h>
+
+#include <deal.II/fe/fe_interface_values.h>
+#include <deal.II/fe/fe_q.h>
+
+#include <deal.II/grid/filtered_iterator.h>
+#include <deal.II/grid/grid_generator.h>
+#include <deal.II/grid/tria_accessor.h>
+#include <deal.II/grid/tria_iterator.h>
+
+#include <deal.II/hp/fe_collection.h>
+
+#include "../tests.h"
+
+
+template <int dim, int spacedim>
+void
+test()
+{
+  Triangulation<dim, spacedim> tria;
+  GridGenerator::hyper_cube(tria, 0, 1, true);
+  tria.refine_global(1);
+
+  const FE_Q<dim, spacedim> fe(1);
+  const QGauss<dim - 1>     quadrature(1);
+
+  DoFHandler<dim, spacedim> dof_handler(tria);
+  dof_handler.distribute_dofs(fe);
+
+  FEInterfaceValues<dim, spacedim> fe_interface_values(fe,
+                                                       quadrature,
+                                                       update_default);
+  const unsigned int invalid_subface = numbers::invalid_unsigned_int;
+  const unsigned int face_index      = 3;
+
+  for (const auto &cell :
+       filter_iterators(dof_handler.active_cell_iterators(),
+                        IteratorFilters::ActiveFEIndexEqualTo(0)))
+    {
+      if (cell == dof_handler.begin_active())
+        {
+          const auto cell_neighbor = cell->neighbor(face_index);
+
+          // This commented out code block identifies that the filtered iterator
+          // is of a different type to that returned by cell->neighbor()
+          //
+          // using C1 = typename std::decay<decltype(cell)>::type;
+          // using C2 = typename std::decay<decltype(cell_neighbor)>::type;
+          // static_assert(std::is_same<C1, C2>::value,
+          //               "Cell iterator types are not identical.");
+
+          fe_interface_values.reinit(cell,
+                                     face_index,
+                                     invalid_subface,
+                                     cell->neighbor(face_index),
+                                     cell->neighbor_of_neighbor(face_index),
+                                     invalid_subface);
+        }
+    }
+
+  for (const auto &cell : dof_handler.active_cell_iterators() |
+                            IteratorFilters::ActiveFEIndexEqualTo(0))
+    {
+      if (cell == dof_handler.begin_active())
+        {
+          fe_interface_values.reinit(cell,
+                                     face_index,
+                                     invalid_subface,
+                                     cell->neighbor(face_index),
+                                     cell->neighbor_of_neighbor(face_index),
+                                     invalid_subface);
+        }
+    }
+}
+
+
+int
+main()
+{
+  initlog();
+
+  test<2, 2>();
+  test<2, 3>();
+  test<3, 3>();
+
+  deallog << "OK" << std::endl;
+}
diff --git a/tests/grid/filtered_iterator_08.output b/tests/grid/filtered_iterator_08.output
new file mode 100644
index 0000000000..0fd8fc12f0
--- /dev/null
+++ b/tests/grid/filtered_iterator_08.output
@@ -0,0 +1,2 @@
+
+DEAL::OK
-- 
2.39.5