diff --git a/Tests/MaterialLib/TestMPL.cpp b/Tests/MaterialLib/TestMPL.cpp
index ff4b43c31c866722d2b46020e67abcdf2e6aca79..0dcb8795121036017dad61cc1dd003596f20de4e 100644
--- a/Tests/MaterialLib/TestMPL.cpp
+++ b/Tests/MaterialLib/TestMPL.cpp
@@ -19,6 +19,8 @@
 #include "MathLib/InterpolationAlgorithms/PiecewiseLinearInterpolation.h"
 #include "ParameterLib/Parameter.h"
 
+namespace Tests
+{
 std::unique_ptr<MPL::Medium> createTestMaterial(std::string const& xml)
 {
     auto const ptree = readXml(xml.c_str());
@@ -33,8 +35,6 @@ std::unique_ptr<MPL::Medium> createTestMaterial(std::string const& xml)
     return MPL::createMedium(config, parameters, nullptr, curves);
 }
 
-namespace Tests
-{
 std::unique_ptr<MaterialPropertyLib::Property> createTestProperty(
     const char xml[],
     std::function<std::unique_ptr<MaterialPropertyLib::Property>(
diff --git a/Tests/MaterialLib/TestMPL.h b/Tests/MaterialLib/TestMPL.h
index 6f5e9584de6a0e06b631b30fc4d3062149e29d9e..c3323f0f650a1422d792ff57b0ec46541da16047 100644
--- a/Tests/MaterialLib/TestMPL.h
+++ b/Tests/MaterialLib/TestMPL.h
@@ -30,10 +30,10 @@ namespace MaterialPropertyLib
 class Property;
 }
 
-std::unique_ptr<MPL::Medium> createTestMaterial(std::string const& xml);
-
 namespace Tests
 {
+std::unique_ptr<MPL::Medium> createTestMaterial(std::string const& xml);
+
 std::unique_ptr<MaterialPropertyLib::Property> createTestProperty(
     const char xml[],
     std::function<std::unique_ptr<MaterialPropertyLib::Property>(
diff --git a/Tests/MaterialLib/TestMPLIdealGasLaw.cpp b/Tests/MaterialLib/TestMPLIdealGasLaw.cpp
index 8bfc3b926374dde4789521fc46844f469f439a54..5f9ab40e291e425bd49d989f5c1cbd107856fb0f 100644
--- a/Tests/MaterialLib/TestMPLIdealGasLaw.cpp
+++ b/Tests/MaterialLib/TestMPLIdealGasLaw.cpp
@@ -56,7 +56,7 @@ TEST(MaterialPropertyLib, IdealGasLawOfPurePhase)
     m << "<properties></properties>\n";
     m << "</medium>\n";
 
-    auto const& medium = createTestMaterial(m.str());
+    auto const& medium = Tests::createTestMaterial(m.str());
     auto const& gas_phase = medium->phase("Gas");
 
     MaterialPropertyLib::VariableArray variable_array;
diff --git a/Tests/MaterialLib/TestMPLParseMaterial.cpp b/Tests/MaterialLib/TestMPLParseMaterial.cpp
index 956c007593f7898b41bed246a4673d9db9b961ff..5171e5d982a1324593077a62bc11246b4b8aa6db 100644
--- a/Tests/MaterialLib/TestMPLParseMaterial.cpp
+++ b/Tests/MaterialLib/TestMPLParseMaterial.cpp
@@ -243,7 +243,7 @@ TEST(Material, parseMaterials)
     medium.property[MPL::permeability] = "1.0e-12";
 
     // create an actual MaterialProperty-Medium out of the specifier object
-    auto const m = createTestMaterial(makeMedium(medium));
+    auto const m = Tests::createTestMaterial(makeMedium(medium));
 
     // those two vectors will actually be compared
     std::vector<std::string> expected;
diff --git a/Tests/MaterialLib/TestMPLRelPermBrooksCorey.cpp b/Tests/MaterialLib/TestMPLRelPermBrooksCorey.cpp
index cbc94cf535d5676e6361863641e9a66057a87f64..209e23310e84874c0d37d63f94774331d648ac91 100644
--- a/Tests/MaterialLib/TestMPLRelPermBrooksCorey.cpp
+++ b/Tests/MaterialLib/TestMPLRelPermBrooksCorey.cpp
@@ -90,7 +90,7 @@ TEST(MaterialPropertyLib, RelPermBrooksCorey)
         std::stringstream m;
         m << m_beg.str() << m_sat.str() << m_end.str();
 
-        auto const& medium = createTestMaterial(m.str());
+        auto const& medium = Tests::createTestMaterial(m.str());
         MaterialPropertyLib::VariableArray variable_array;
         ParameterLib::SpatialPosition const pos;
         double const time = std::numeric_limits<double>::quiet_NaN();
diff --git a/Tests/MaterialLib/TestMPLRelPermLiakopoulos.cpp b/Tests/MaterialLib/TestMPLRelPermLiakopoulos.cpp
index 87c314c722370572a94fcaa56fdfaf1018ffec64..290d6eb9e982551d17ca38b9521c39c7d18f5e78 100644
--- a/Tests/MaterialLib/TestMPLRelPermLiakopoulos.cpp
+++ b/Tests/MaterialLib/TestMPLRelPermLiakopoulos.cpp
@@ -77,7 +77,7 @@ TEST(MaterialPropertyLib, RelPermLiakopoulos)
         std::stringstream m;
         m << m_beg.str() << m_sat.str() << m_end.str();
 
-        auto const& medium = createTestMaterial(m.str());
+        auto const& medium = Tests::createTestMaterial(m.str());
         MaterialPropertyLib::VariableArray variable_array;
         ParameterLib::SpatialPosition const pos;
         double const time = std::numeric_limits<double>::quiet_NaN();
diff --git a/Tests/MaterialLib/TestMPLSaturationBrooksCorey.cpp b/Tests/MaterialLib/TestMPLSaturationBrooksCorey.cpp
index 4dfa8a9f92f826d9c32fc995ed0672749531ec5d..4193ddbe7fb789facf2a7708bafa2482b82f3017 100644
--- a/Tests/MaterialLib/TestMPLSaturationBrooksCorey.cpp
+++ b/Tests/MaterialLib/TestMPLSaturationBrooksCorey.cpp
@@ -43,7 +43,7 @@ TEST(MaterialPropertyLib, SaturationBrooksCorey)
     m << "</properties>\n";
     m << "</medium>\n";
 
-    auto const& medium = createTestMaterial(m.str());
+    auto const& medium = Tests::createTestMaterial(m.str());
 
     MaterialPropertyLib::VariableArray variable_array;
     ParameterLib::SpatialPosition const pos;
diff --git a/Tests/MaterialLib/TestMPLSaturationLiakopoulos.cpp b/Tests/MaterialLib/TestMPLSaturationLiakopoulos.cpp
index f64b1c560bb728c879655cdfa6718ab8886f4d6a..5255e4532659e4525dc8d71fbf92539291f5d4c6 100644
--- a/Tests/MaterialLib/TestMPLSaturationLiakopoulos.cpp
+++ b/Tests/MaterialLib/TestMPLSaturationLiakopoulos.cpp
@@ -30,7 +30,7 @@ TEST(MaterialPropertyLib, SaturationLiakopoulos)
     m << "</properties>\n";
     m << "</medium>\n";
 
-    auto const& medium = createTestMaterial(m.str());
+    auto const& medium = Tests::createTestMaterial(m.str());
 
     MaterialPropertyLib::VariableArray variable_array;
     ParameterLib::SpatialPosition const pos;