[T/MaterialPropertyLib] Test for LinearProperties.

Tests/MaterialLib/TestMPLLinearProperty.cpp

+/**
+ * \file
+ *
+ * \copyright
+ * Copyright (c) 2012-2019, 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 "MaterialLib/MPL/Properties/LinearProperty.h"
+
+TEST(MaterialPropertyLib, LinearProperty)
+{
+    double const y_ref = 1.0;
+    double const m = 1.0;
+    double const x_ref = 293.15;
+    MaterialPropertyLib::IndependentVariable const iv{
+        MaterialPropertyLib::Variables::temperature, x_ref, m};
+    MaterialPropertyLib::LinearProperty linear_property{y_ref, iv};
+
+    MaterialPropertyLib::VariableArray variable_array;
+    variable_array[MaterialPropertyLib::Variables::temperature] = 303.15;
+    ASSERT_NEAR(
+        boost::get<double>(linear_property.value(variable_array)),
+        y_ref + m * (boost::get<double>(
+                         variable_array
+                             [MaterialPropertyLib::Variables::temperature]) -
+                     x_ref),
+        1.e-10);
+    ASSERT_EQ(
+        boost::get<double>(linear_property.dValue(
+            variable_array, MaterialPropertyLib::Variables::phase_pressure)),
+        0.0);
+    ASSERT_EQ(boost::get<double>(linear_property.dValue(
+                  variable_array, MaterialPropertyLib::Variables::temperature)),
+              m);
+    ASSERT_EQ(boost::get<double>(linear_property.d2Value(
+                  variable_array,
+                  MaterialPropertyLib::Variables::temperature,
+                  MaterialPropertyLib::Variables::temperature)),
+              0.0);
+}
+