added unit test for duplicate cells

Author: MohamedElkamash

tests/cpp_unit_tests/CMakeLists.txt

@@ -8,6 +8,7 @@ set(TEST_NAMES
   test_mesh
   test_region
   test_tensor
+  test_surf_source_write
   # Add additional unit test files here
 )
 

tests/cpp_unit_tests/test_surf_source_write.cpp

@@ -0,0 +1,105 @@
+#include <string>
+#include <vector>
+
+#include <catch2/catch_test_macros.hpp>
+#include <pugixml.hpp>
+
+#include "openmc/settings.h"
+
+auto ssw_cells_from_xml(std::string xml_string) {
+
+    // Create a pugixml document object
+    pugi::xml_document doc;
+
+    // Load the XML from the string
+    pugi::xml_parse_result result = doc.load_string(xml_string.c_str());
+    
+    pugi::xml_node root = doc.child("settings");
+
+    // Read the surface source settings
+    openmc::read_settings_xml(root);
+
+    // Get the cell direction map
+    auto ssw_cells = openmc::settings::ssw_cells;
+
+    // Finalize to allow more tests
+    openmc::free_memory_settings();
+    openmc::settings::n_particles = -1;
+    openmc::settings::run_mode = openmc::RunMode::UNSET;
+
+    return ssw_cells;
+}
+
+TEST_CASE("Test duplicate cells in surface source write")
+{
+  std::vector<std::string> xml_strings = {
+    R"(
+        <settings>
+          <run_mode>fixed source</run_mode>
+          <particles>60</particles>
+          <batches>1</batches>
+          <surf_source_write>
+            <surface_ids>1</surface_ids>
+            <max_particles>300</max_particles>
+            <cells>1 1</cells>
+            <directions>to to</directions>
+          </surf_source_write>
+        </settings>
+    )",
+    R"(
+        <settings>
+          <run_mode>fixed source</run_mode>
+          <particles>60</particles>
+          <batches>1</batches>
+          <surf_source_write>
+            <surface_ids>1</surface_ids>
+            <max_particles>300</max_particles>
+            <cells>1 1</cells>
+            <directions>to from</directions>
+          </surf_source_write>
+        </settings>
+    )",
+    R"(
+        <settings>
+          <run_mode>fixed source</run_mode>
+          <particles>60</particles>
+          <batches>1</batches>
+          <surf_source_write>
+            <surface_ids>1</surface_ids>
+            <max_particles>300</max_particles>
+            <cells>1 1</cells>
+            <directions>to both</directions>
+          </surf_source_write>
+        </settings>
+    )",
+    R"(
+        <settings>
+          <run_mode>fixed source</run_mode>
+          <particles>60</particles>
+          <batches>1</batches>
+          <surf_source_write>
+            <surface_ids>1</surface_ids>
+            <max_particles>300</max_particles>
+            <cells>1 1</cells>
+            <directions>both to</directions>
+          </surf_source_write>
+        </settings>
+    )"
+  };
+
+  auto ssw_cells = ssw_cells_from_xml(xml_strings[0]);
+  REQUIRE(ssw_cells.size() == 1);
+  REQUIRE(ssw_cells.at(1) == openmc::SSWCellType::To);
+
+  ssw_cells = ssw_cells_from_xml(xml_strings[1]);
+  REQUIRE(ssw_cells.size() == 1);
+  REQUIRE(ssw_cells.at(1) == openmc::SSWCellType::Both);
+
+  ssw_cells = ssw_cells_from_xml(xml_strings[2]);
+  REQUIRE(ssw_cells.size() == 1);
+  REQUIRE(ssw_cells.at(1) == openmc::SSWCellType::Both);
+
+  ssw_cells = ssw_cells_from_xml(xml_strings[3]);
+  REQUIRE(ssw_cells.size() == 1);
+  REQUIRE(ssw_cells.at(1) == openmc::SSWCellType::Both);
+}