[T] add a unit test.

Tests/CMakeLists.txt

@@ -46,6 +46,10 @@ if(OGS_BUILD_SWMM)
     append_source_files(TEST_SOURCES FileIO_SWMM)
 endif()
 
+if(OGS_BUILD_PROCESS_ComponentTransport)
+    append_source_files(TEST_SOURCES ProcessLib/ComponentTransport)
+endif()
+
 if(OGS_BUILD_PROCESS_RichardsMechanics)
     append_source_files(TEST_SOURCES ProcessLib/RichardsMechanics)
 endif()

Tests/Data/FileIO/sparse_table.txt

+Ni	Np(5)	Th	Ra	Ni_prev	Np(5)_prev	Th_prev	Ra_prev	Ni_new	Np(5)_new	Th_new	Ra_new
+1e-5	1e-6	1e-7	1e-8	1e-9	1e-10	1e-11	1e-12	0.000000000000e+00	0.000000000000e+00	0.000000000000e+00	9.977098263915e-13

Tests/ProcessLib/ComponentTransport/TestLookupTable.cpp

+/**
+ * \copyright
+ * Copyright (c) 2012-2021, OpenGeoSys Community (http://www.opengeosys.org)
+ *            Distributed under a Modified BSD License.
+ *              See accompanying file LICENSE.txt or
+ *              http://www.opengeosys.org/project/license
+ */
+
+#include <gtest/gtest.h>
+
+#include <Eigen/Eigen>
+#include <cmath>
+#include <memory>
+
+#include "BaseLib/FileTools.h"
+#include "InfoLib/TestInfo.h"
+#include "MeshLib/Mesh.h"
+#include "MeshLib/MeshGenerators/MeshGenerator.h"
+#include "ProcessLib/ComponentTransport/CreateLookupTable.h"
+#include "ProcessLib/ComponentTransport/LookupTable.h"
+#include "ProcessLib/ProcessVariable.h"
+#include "Tests/TestTools.h"
+
+using namespace ProcessLib::ComponentTransport;
+
+namespace
+{
+std::unique_ptr<LookupTable> createTestLookupTable(const char xml[])
+{
+    auto const ptree = Tests::readXml(xml);
+    BaseLib::ConfigTree conf(ptree, "", BaseLib::ConfigTree::onerror,
+                             BaseLib::ConfigTree::onwarning);
+
+    std::vector<std::unique_ptr<MeshLib::Mesh>> meshes;
+    {
+        std::size_t const n_elements = 4;
+        auto mesh = std::unique_ptr<MeshLib::Mesh>(
+            MeshLib::MeshGenerator::generateRegularQuadMesh(1.0, n_elements));
+        meshes.push_back(std::move(mesh));
+    }
+
+    std::map<std::string,
+             std::unique_ptr<MathLib::PiecewiseLinearInterpolation>>
+        curves;
+
+    std::vector<std::unique_ptr<ParameterLib::ParameterBase>> parameters;
+    {
+        auto const& para_config = conf.getConfigSubtree("parameter");
+        auto p = ParameterLib::createParameter(para_config, meshes, curves);
+        parameters.push_back(std::move(p));
+    }
+
+    std::vector<ProcessLib::ProcessVariable> variables;
+    auto const& process_variables_config =
+        conf.getConfigSubtree("process_variables");
+    for (auto var_config :
+         process_variables_config.getConfigSubtreeList("process_variable"))
+    {
+        variables.emplace_back(var_config, *meshes[0], meshes, parameters,
+                               curves);
+    }
+
+    std::vector<
+        std::vector<std::reference_wrapper<ProcessLib::ProcessVariable>>>
+        process_variables;
+    {
+        for (auto& pv : variables)
+        {
+            std::vector<std::reference_wrapper<ProcessLib::ProcessVariable>>
+                per_process_variable;
+
+            per_process_variable.push_back(pv);
+            process_variables.push_back(std::move(per_process_variable));
+        }
+    }
+
+    std::optional<std::string> file_name(TestInfoLib::TestInfo::data_path +
+                                         "/FileIO/sparse_table.txt");
+    if (!BaseLib::isProjectDirectorySet())
+    {
+        BaseLib::setProjectDirectory(BaseLib::extractPath(*file_name));
+    }
+
+    return createLookupTable(file_name, process_variables);
+}
+
+}  // namespace
+
+TEST(ComponentTransport, checkLookupTable)
+{
+    const char xml[] =
+        "<parameter>"
+        "     <name>c0</name>"
+        "     <type>Constant</type>"
+        "     <value>0</value>"
+        "</parameter>"
+        "<process_variables>"
+        "    <process_variable>"
+        "        <name>Ni</name>"
+        "        <components>1</components>"
+        "        <order>1</order>"
+        "        <initial_condition>c0</initial_condition>"
+        "        <boundary_conditions>"
+        "        </boundary_conditions>"
+        "    </process_variable>"
+        "    <process_variable>"
+        "        <name>Np(5)</name>"
+        "        <components>1</components>"
+        "        <order>1</order>"
+        "        <initial_condition>c0</initial_condition>"
+        "        <boundary_conditions>"
+        "        </boundary_conditions>"
+        "    </process_variable>"
+        "    <process_variable>"
+        "        <name>Th</name>"
+        "        <components>1</components>"
+        "        <order>1</order>"
+        "        <initial_condition>c0</initial_condition>"
+        "        <boundary_conditions>"
+        "        </boundary_conditions>"
+        "    </process_variable>"
+        "    <process_variable>"
+        "        <name>Ra</name>"
+        "        <components>1</components>"
+        "        <order>1</order>"
+        "        <initial_condition>c0</initial_condition>"
+        "        <boundary_conditions>"
+        "        </boundary_conditions>"
+        "    </process_variable>"
+        "</process_variables>";
+
+    auto const lookup_table = createTestLookupTable(xml);
+    auto const& tabular_data = lookup_table->tabular_data;
+
+    ASSERT_EQ(1.e-5, tabular_data.at("Ni")[0]);
+    ASSERT_EQ(1e-9, tabular_data.at("Ni_prev")[0]);
+    ASSERT_EQ(0., tabular_data.at("Ni_new")[0]);
+
+    ASSERT_EQ(1.e-6, tabular_data.at("Np(5)")[0]);
+    ASSERT_EQ(1.e-10, tabular_data.at("Np(5)_prev")[0]);
+    ASSERT_EQ(0., tabular_data.at("Np(5)_new")[0]);
+
+    ASSERT_EQ(1.e-7, tabular_data.at("Th")[0]);
+    ASSERT_EQ(1.e-11, tabular_data.at("Th_prev")[0]);
+    ASSERT_EQ(0., tabular_data.at("Th_new")[0]);
+
+    ASSERT_EQ(1.e-8, tabular_data.at("Ra")[0]);
+    ASSERT_EQ(1.e-12, tabular_data.at("Ra_prev")[0]);
+    ASSERT_EQ(9.977098263915e-13, tabular_data.at("Ra_new")[0]);
+}