[T/Mat] Fix fluid property tests.

Tests/MaterialLib/TestFluidProperties.cpp

@@ -63,8 +63,10 @@ TEST(MaterialFluidProperties, checkPrimaryVariableDependentFluidProperties)
     ASSERT_NEAR(mu_expected,
                 fluid_model->getValue(FluidPropertyType::Viscosity, vars),
                 1.e-10);
+    const double dmu_dT_expected =
+        -1.e-3/368 * std::exp(-(vars[0] - 293) / 368);
     ASSERT_NEAR(
-        -mu_expected,
+        dmu_dT_expected,
         fluid_model->getdValue(FluidPropertyType::Viscosity, vars,
                                MaterialLib::Fluid::PropertyVariableType::T),
         1.e-10);

Tests/MaterialLib/TestFluidViscosity.cpp

@@ -64,8 +64,10 @@ TEST(Material, checkTemperatureDependentViscosity)
     vars[0] = 350.0;
     const double mu_expected = 1.e-3 * std::exp(-(vars[0] - 293) / 368);
     ASSERT_NEAR(mu_expected, mu->getValue(vars), 1.e-10);
+    const double dmu_dT_expected =
+        -1.e-3/368 * std::exp(-(vars[0] - 293) / 368);
     ASSERT_NEAR(
-        -mu_expected,
+        dmu_dT_expected,
         mu->getdValue(vars, MaterialLib::Fluid::PropertyVariableType::T),
         1.e-10);
 }