diff --git a/test/TestUtils.cpp b/test/TestUtils.cpp
index 71eeadb3a..6222955d5 100644
--- a/test/TestUtils.cpp
+++ b/test/TestUtils.cpp
@@ -19,8 +19,6 @@
  * @date 2015
  */
 
-#include <ctime>
-#include <random>
 #include <thread>
 #include <boost/test/unit_test.hpp>
 #include <boost/filesystem.hpp>
@@ -28,10 +26,6 @@
 #include <libtestutils/FixedClient.h>
 #include "TestUtils.h"
 
-// used methods from TestHelper:
-// getTestPath
-#include "TestHelper.h"
-
 using namespace std;
 using namespace dev;
 using namespace dev::eth;
@@ -73,19 +67,12 @@ std::string dev::test::getCommandLineArgument(string const& _name, bool _require
 	return "";
 }
 
-bool LoadTestFileFixture::m_loaded = false;
-Json::Value LoadTestFileFixture::m_json;
-
 LoadTestFileFixture::LoadTestFileFixture()
 {
-	if (!m_loaded)
-	{
-		m_json = loadJsonFromFile(toTestFilePath(getCommandLineArgument("--eth_testfile")));
-		m_loaded = true;
-	}
+	m_json = loadJsonFromFile(toTestFilePath(getCommandLineArgument("--eth_testfile")));
 }
 
-void ParallelFixture::enumerateThreads(std::function<void()> callback)
+void ParallelFixture::enumerateThreads(std::function<void()> callback) const
 {
 	size_t threadsCount = std::stoul(getCommandLineArgument("--eth_threads"), nullptr, 10);
 	
@@ -99,7 +86,7 @@ void ParallelFixture::enumerateThreads(std::function<void()> callback)
 	});
 }
 
-void BlockChainFixture::enumerateBlockchains(std::function<void(Json::Value const&, dev::eth::BlockChain&, State state)> callback)
+void BlockChainFixture::enumerateBlockchains(std::function<void(Json::Value const&, dev::eth::BlockChain const&, State state)> callback) const
 {
 	for (string const& name: m_json.getMemberNames())
 	{
@@ -108,16 +95,16 @@ void BlockChainFixture::enumerateBlockchains(std::function<void(Json::Value cons
 	}
 }
 
-void ClientBaseFixture::enumerateClients(std::function<void(Json::Value const&, dev::eth::ClientBase&)> callback)
+void ClientBaseFixture::enumerateClients(std::function<void(Json::Value const&, dev::eth::ClientBase&)> callback) const
 {
-	enumerateBlockchains([&callback](Json::Value const& _json, BlockChain& _bc, State _state) -> void
+	enumerateBlockchains([&callback](Json::Value const& _json, BlockChain const& _bc, State _state) -> void
 	{
 		FixedClient client(_bc, _state);
 		callback(_json, client);
 	});
 }
 
-void ParallelClientBaseFixture::enumerateClients(std::function<void(Json::Value const&, dev::eth::ClientBase&)> callback)
+void ParallelClientBaseFixture::enumerateClients(std::function<void(Json::Value const&, dev::eth::ClientBase&)> callback) const
 {
 	ClientBaseFixture::enumerateClients([this, &callback](Json::Value const& _json, dev::eth::ClientBase& _client) -> void
 	{
diff --git a/test/TestUtils.h b/test/TestUtils.h
index fef10e982..f9817c21d 100644
--- a/test/TestUtils.h
+++ b/test/TestUtils.h
@@ -41,24 +41,24 @@ static SharedMutex x_boostTest;
 struct LoadTestFileFixture
 {
 	LoadTestFileFixture();
-	
-	static bool m_loaded;
-	static Json::Value m_json;
+
+protected:
+	Json::Value m_json;
 };
 
 struct ParallelFixture
 {
-	void enumerateThreads(std::function<void()> callback);
+	void enumerateThreads(std::function<void()> callback) const;
 };
 
 struct BlockChainFixture: public LoadTestFileFixture
 {
-	void enumerateBlockchains(std::function<void(Json::Value const&, dev::eth::BlockChain&, dev::eth::State state)> callback);
+	void enumerateBlockchains(std::function<void(Json::Value const&, dev::eth::BlockChain const&, dev::eth::State state)> callback) const;
 };
 
 struct ClientBaseFixture: public BlockChainFixture
 {
-	void enumerateClients(std::function<void(Json::Value const&, dev::eth::ClientBase&)> callback);
+	void enumerateClients(std::function<void(Json::Value const&, dev::eth::ClientBase&)> callback) const;
 };
 
 // important BOOST TEST do have problems with thread safety!!!
@@ -70,7 +70,7 @@ struct ClientBaseFixture: public BlockChainFixture
 // https://codecrafter.wordpress.com/2012/11/01/c-unit-test-framework-adapter-part-3/
 struct ParallelClientBaseFixture: public ClientBaseFixture, public ParallelFixture
 {
-	void enumerateClients(std::function<void(Json::Value const&, dev::eth::ClientBase&)> callback);
+	void enumerateClients(std::function<void(Json::Value const&, dev::eth::ClientBase&)> callback) const;
 };
 
 struct JsonRpcFixture: public ClientBaseFixture