diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..7dc790c
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,3 @@
+[submodule "tests/googletest"]
+	path = tests/googletest
+	url = https://github.com/google/googletest
diff --git a/src/log.cpp b/src/log.cpp
index 81c9fc3..5987608 100644
--- a/src/log.cpp
+++ b/src/log.cpp
@@ -234,7 +234,9 @@ private:
 	std::ofstream m_logFile;
 };
 
+#ifndef P2POOL_LOG_DISABLE
 static Worker worker;
+#endif
 
 NOINLINE Writer::Writer(Severity severity) : Stream(m_stackBuf)
 {
@@ -252,7 +254,9 @@ NOINLINE Writer::~Writer()
 	m_buf[1] = static_cast<uint8_t>(size & 255);
 	m_buf[2] = static_cast<uint8_t>(size >> 8);
 	m_buf[m_pos] = '\n';
+#ifndef P2POOL_LOG_DISABLE
 	worker.write(m_buf, size);
+#endif
 }
 
 void reopen()
@@ -263,7 +267,9 @@ void reopen()
 
 void stop()
 {
+#ifndef P2POOL_LOG_DISABLE
 	worker.stop();
+#endif
 }
 
 NOINLINE void Stream::writeCurrentTime()
diff --git a/src/log.h b/src/log.h
index 5183a68..dac0860 100644
--- a/src/log.h
+++ b/src/log.h
@@ -384,6 +384,14 @@ namespace {
 #define CONCAT(a, b) CONCAT2(a, b)
 #define CONCAT2(a, b) a##b
 
+#ifdef P2POOL_LOG_DISABLE
+
+#define LOGINFO(level, ...)
+#define LOGWARN(level, ...)
+#define LOGERR(level, ...)
+
+#else
+
 #define LOG(level, severity, ...) \
 	do { \
 		if (level <= log::GLOBAL_LOG_LEVEL) { \
@@ -398,6 +406,8 @@ namespace {
 #define LOGWARN(level, ...) LOG(level, log::Severity::Warning, __VA_ARGS__)
 #define LOGERR(level, ...)  LOG(level, log::Severity::Error, __VA_ARGS__)
 
+#endif
+
 void reopen();
 void stop();
 
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
new file mode 100644
index 0000000..15e637d
--- /dev/null
+++ b/tests/CMakeLists.txt
@@ -0,0 +1,108 @@
+cmake_minimum_required(VERSION 2.8.12)
+project(p2pool_tests)
+
+add_subdirectory(googletest)
+set(LIBS gtest)
+
+if (CMAKE_CXX_COMPILER_ID MATCHES GNU)
+	set(WARNING_FLAGS "")
+	set(OPTIMIZATION_FLAGS "-Ofast -s")
+
+	set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${WARNING_FLAGS}")
+	set(CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE} ${WARNING_FLAGS} ${OPTIMIZATION_FLAGS}")
+
+	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${WARNING_FLAGS}")
+	set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} ${WARNING_FLAGS} ${OPTIMIZATION_FLAGS}")
+
+	if (WIN32)
+		set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -static")
+	else()
+		if (STATIC_LINUX_BINARY)
+			set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -static")
+		else()
+			set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -static-libgcc -static-libstdc++")
+		endif()
+	endif()
+elseif (CMAKE_CXX_COMPILER_ID MATCHES MSVC)
+	set(WARNING_FLAGS "")
+	set(SECURITY_FLAGS "/GS /guard:cf")
+	set(OPTIMIZATION_FLAGS "/O2 /Oi /Ob2 /Ot /DNDEBUG /GL")
+
+	set(CMAKE_C_FLAGS_DEBUG "${WARNING_FLAGS} ${SECURITY_FLAGS} /Od /Ob0 /Zi /MTd /fsanitize=address")
+	set(CMAKE_CXX_FLAGS_DEBUG "${WARNING_FLAGS} ${SECURITY_FLAGS} /Od /Ob0 /Zi /MTd /fsanitize=address")
+
+	set(CMAKE_C_FLAGS_RELEASE "${WARNING_FLAGS} ${SECURITY_FLAGS} ${OPTIMIZATION_FLAGS} /MT")
+	set(CMAKE_CXX_FLAGS_RELEASE "${WARNING_FLAGS} ${SECURITY_FLAGS} ${OPTIMIZATION_FLAGS} /MT")
+
+	set(CMAKE_C_FLAGS_RELWITHDEBINFO "${WARNING_FLAGS} ${SECURITY_FLAGS} /Ob1 /Ot /Zi /MT")
+	set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "${WARNING_FLAGS} ${SECURITY_FLAGS} /Ob1 /Ot /Zi /MT")
+elseif (CMAKE_CXX_COMPILER_ID MATCHES Clang)
+	set(WARNING_FLAGS "")
+	set(OPTIMIZATION_FLAGS "-Ofast -funroll-loops -fmerge-all-constants")
+
+	set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${WARNING_FLAGS}")
+	set(CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE} ${WARNING_FLAGS} ${OPTIMIZATION_FLAGS}")
+
+	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${WARNING_FLAGS}")
+	set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} ${WARNING_FLAGS} ${OPTIMIZATION_FLAGS}")
+endif()
+
+set(HEADERS
+)
+
+set(SOURCES
+	src/difficulty_type.cpp
+	src/tests.cpp
+	../src/log.cpp
+	../src/util.cpp
+)
+
+include_directories(../src)
+include_directories(../external/src)
+include_directories(../external/src/cryptonote)
+include_directories(../external/src/libuv/include)
+include_directories(../external/src/cppzmq)
+include_directories(../external/src/libzmq/include)
+include_directories(../external/src/llhttp)
+include_directories(../external/src/randomx/src)
+include_directories(src)
+include_directories(googletest/googletest/include)
+
+if (WIN32)
+	set(LIBS ${LIBS} ws2_32 iphlpapi userenv psapi)
+elseif (NOT APPLE)
+	set(LIBS ${LIBS} pthread gss dl)
+endif()
+
+if (CMAKE_CXX_COMPILER_ID MATCHES MSVC)
+	find_library(ZMQ_LIBRARY_DEBUG NAMES libzmq-v142-mt-sgd-4_3_5 PATHS "../external/lib/libzmq/Debug")
+	find_library(ZMQ_LIBRARY NAMES libzmq-v142-mt-s-4_3_5 PATHS "../external/lib/libzmq/Release")
+	find_library(UV_LIBRARY_DEBUG NAMES uv_a PATHS "../external/lib/libuv/Debug")
+	find_library(UV_LIBRARY NAMES uv_a PATHS "../external/lib/libuv/Release")
+elseif (CMAKE_CXX_COMPILER_ID MATCHES GNU OR CMAKE_CXX_COMPILER_ID MATCHES Clang)
+	find_library(ZMQ_LIBRARY_DEBUG NAMES zmq libzmq.a)
+	find_library(ZMQ_LIBRARY NAMES zmq libzmq.a)
+	find_library(UV_LIBRARY_DEBUG NAMES uv libuv.a)
+	find_library(UV_LIBRARY NAMES uv libuv.a)
+	find_library(SODIUM_LIBRARY sodium)
+endif()
+
+find_library(PGM_LIBRARY pgm)
+find_library(NORM_LIBRARY norm)
+
+if (PGM_LIBRARY)
+	set(LIBS ${LIBS} ${PGM_LIBRARY})
+endif()
+
+if (NORM_LIBRARY)
+	set(LIBS ${LIBS} ${NORM_LIBRARY})
+endif()
+
+if (SODIUM_LIBRARY)
+	set(LIBS ${LIBS} ${SODIUM_LIBRARY})
+endif()
+
+add_definitions(/DZMQ_STATIC /DP2POOL_LOG_DISABLE)
+
+add_executable(${CMAKE_PROJECT_NAME} ${HEADERS} ${SOURCES})
+target_link_libraries(${CMAKE_PROJECT_NAME} debug ${ZMQ_LIBRARY_DEBUG} debug ${UV_LIBRARY_DEBUG} optimized ${ZMQ_LIBRARY} optimized ${UV_LIBRARY} ${LIBS})
diff --git a/tests/googletest b/tests/googletest
new file mode 160000
index 0000000..955c7f8
--- /dev/null
+++ b/tests/googletest
@@ -0,0 +1 @@
+Subproject commit 955c7f837efad184ec63e771c42542d37545eaef
diff --git a/tests/src/difficulty_type.cpp b/tests/src/difficulty_type.cpp
new file mode 100644
index 0000000..dbeb6bb
--- /dev/null
+++ b/tests/src/difficulty_type.cpp
@@ -0,0 +1,248 @@
+/*
+ * This file is part of the Monero P2Pool <https://github.com/SChernykh/p2pool>
+ * Copyright (c) 2021 SChernykh <https://github.com/SChernykh>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "common.h"
+#include "gtest/gtest.h"
+#include <random>
+
+namespace p2pool {
+
+TEST(difficulty_type, target)
+{
+	// diff = 0
+	{
+		difficulty_type d(0, 0);
+		ASSERT_EQ(d.target(), std::numeric_limits<uint64_t>::max());
+	}
+
+	// diff = 1
+	{
+		difficulty_type d(1, 0);
+		ASSERT_EQ(d.target(), std::numeric_limits<uint64_t>::max());
+	}
+
+	// diff = 2^64
+	{
+		difficulty_type d(0, 1);
+		ASSERT_EQ(d.target(), 1);
+	}
+
+	// diff = 2^32
+	{
+		difficulty_type d(1ull << 32, 0);
+		ASSERT_EQ(d.target(), 1ull << 32);
+	}
+
+	// diff from block 2440918
+	{
+		difficulty_type d(334654765825ull, 0);
+		ASSERT_EQ(d.target(), 55121714);
+	}
+}
+
+TEST(difficulty_type, sum)
+{
+	// No carry
+	{
+		difficulty_type diff[4] = { { 0, 0 }, { 1, 0 }, { 0, 1 }, { 1, 1 } };
+
+		for (int i = 0; i <= 3; ++i) {
+			for (int j = 0; j <= 3; ++j) {
+				difficulty_type a = diff[i];
+				a += diff[j];
+				ASSERT_EQ(a.lo, diff[i].lo + diff[j].lo);
+				ASSERT_EQ(a.hi, diff[i].hi + diff[j].hi);
+			}
+		}
+	}
+
+	// Carry
+	{
+		difficulty_type a(11400714819323198485ull, 0);
+		difficulty_type b(15975348984942515101ull, 0);
+		a += b;
+		ASSERT_EQ(a.lo, 8929319730556161970ull);
+		ASSERT_EQ(a.hi, 1);
+	}
+
+	// Carry (edge case)
+	{
+		difficulty_type a(std::numeric_limits<uint64_t>::max(), 0);
+		difficulty_type b(1, 0);
+		a += b;
+		ASSERT_EQ(a.lo, 0);
+		ASSERT_EQ(a.hi, 1);
+	}
+}
+
+TEST(difficulty_type, compare)
+{
+	const difficulty_type diff[4] = { { 0, 0 }, { 1, 0 }, { 0, 1 }, { 1, 1 } };
+
+	for (int i = 0; i <= 3; ++i) {
+		for (int j = 0; j <= 3; ++j) {
+			ASSERT_EQ(diff[i] <  diff[j], i <  j);
+			ASSERT_EQ(diff[i] >= diff[j], i >= j);
+			ASSERT_EQ(diff[i] == diff[j], i == j);
+			ASSERT_EQ(diff[i] != diff[j], i != j);
+		}
+	}
+}
+
+TEST(difficulty_type, check_pow)
+{
+	hash h;
+
+	// Power of 2 close to the current Monero network difficulty
+	difficulty_type diff = { 1ull << 38, 0 };
+	{
+		// 2^256 / 2^38 = 2^218
+		// diff.check_pow() will get 2^256 as a multiplication result = lowest possible value that fails the test
+		uint64_t data[4] = { 0, 0, 0, 1ull << 26 };
+		memcpy(h.h, data, HASH_SIZE);
+		ASSERT_EQ(diff.check_pow(h), false);
+
+		// Now decrease the hash by 1. It should pass the test now
+		data[0] = data[1] = data[2] = std::numeric_limits<uint64_t>::max();
+		--data[3];
+		memcpy(h.h, data, HASH_SIZE);
+		ASSERT_EQ(diff.check_pow(h), true);
+	}
+
+	/*
+	* Factors of 2^256 - 1:
+	* P1 = 3
+	* P1 = 5
+	* P2 = 17
+	* P3 = 257
+	* P3 = 641
+	* P5 = 65537
+	* P6 = 274177
+	* P7 = 6700417
+	* P14 = 67280421310721
+	* P17 = 59649589127497217
+	* P22 = 5704689200685129054721
+	*/
+	diff = { 67280421310721ull, 0 };
+	{
+		// (2^256 - 1) / 67280421310721 = 1721036922503113971692907638171526209875755521904893141463060735
+		// diff.check_pow() will get 2^256-1 as a multiplication result = highest possible value that still passes the test
+		uint64_t data[4] = { 0xfffffffffffbd0ffull, 0x0000000000042f00ull, 0xfffffffffffbd0ffull, 0x42f00ull };
+		memcpy(h.h, data, HASH_SIZE);
+		ASSERT_EQ(diff.check_pow(h), true);
+
+		// Now increase the hash by 1. It should not pass the test anymore
+		++data[0];
+		memcpy(h.h, data, HASH_SIZE);
+		ASSERT_EQ(diff.check_pow(h), false);
+	}
+
+	// diff = 5704689200685129054721
+	diff = { 4645281908877605377ull, 309ull };
+	{
+		// (2^256 - 1) / 5704689200685129054721 = 20297703374166229616474325006177763232573806344580020735
+		// diff.check_pow() will get 2^256-1 as a multiplication result = highest possible value that still passes the test
+		uint64_t data[4] = { 0xff2c1503c50eb9ffull, 0xffffffffffffffffull, 0xd3eafc3af14600ull, 0 };
+		memcpy(h.h, data, HASH_SIZE);
+		ASSERT_EQ(diff.check_pow(h), true);
+
+		// Now increase the hash by 1. It should not pass the test anymore
+		++data[0];
+		memcpy(h.h, data, HASH_SIZE);
+		ASSERT_EQ(diff.check_pow(h), false);
+	}
+
+	/*
+	* Factors of 2^256 + 1:
+	* P16 = 1238926361552897
+	* P62 = 93461639715357977769163558199606896584051237541638188580280321
+	*/
+	diff = { 1238926361552897ull, 0 };
+	{
+		// (2^256 + 1) / 1238926361552897 = 93461639715357977769163558199606896584051237541638188580280321
+		// diff.check_pow() will get 2^256+1 as a multiplication result = lowest possible non-power of 2 that fails the test
+		uint64_t data[4] = { 0x49baa0ba2c911801ull, 0x6ee3637cab2586d0ull, 0x4c585a8f5c7073e3, 0x3a29ull };
+		memcpy(h.h, data, HASH_SIZE);
+		ASSERT_EQ(diff.check_pow(h), false);
+
+		// Now decrease the hash by 1. It should pass the test now
+		--data[0];
+		memcpy(h.h, data, HASH_SIZE);
+		ASSERT_EQ(diff.check_pow(h), true);
+	}
+
+	// Randomized tests with fixed seed
+	std::mt19937_64 r(0);
+
+	for (int i = 0; i < 1000; ++i) {
+		// Random difficulty between 300G and 400G
+		difficulty_type diff{ 300000000000ull + (r() % 100000000000ull), 0 };
+		hash h;
+
+		// All zeros
+		memset(h.h, 0, HASH_SIZE);
+		ASSERT_EQ(diff.check_pow(h), true);
+
+		// All ones
+		memset(h.h, -1, HASH_SIZE);
+		ASSERT_EQ(diff.check_pow(h), false);
+
+		{
+			uint64_t data[4];
+			uint64_t rem;
+			data[3] = udiv128(1, 0, diff.lo, &rem);
+			data[2] = udiv128(rem, 0, diff.lo, &rem);
+			data[1] = udiv128(rem, 0, diff.lo, &rem);
+			data[0] = udiv128(rem, 0, diff.lo, &rem);
+
+			// Max hash value that passes this difficulty
+			memcpy(h.h, data, HASH_SIZE);
+			EXPECT_EQ(diff.check_pow(h), true);
+
+			// Add 1 to data (256-bit number)
+			for (int j = 0; j <= 3; ++j) {
+				++data[j];
+				if (data[j]) {
+					// No carry, exit the loop
+					break;
+				}
+			}
+
+			// Min hash value that fails this difficulty
+			memcpy(h.h, data, HASH_SIZE);
+			EXPECT_EQ(diff.check_pow(h), false);
+		}
+
+		const uint64_t target = diff.target();
+
+		// Random values that pass
+		for (int j = 0; j < 10000; ++j) {
+			const uint64_t data[4] = { r(), r(), r(), r() % target };
+			memcpy(h.h, data, HASH_SIZE);
+			EXPECT_EQ(diff.check_pow(h), true);
+		}
+
+		// Random values that fail
+		for (int j = 0; j < 10000; ++j) {
+			const uint64_t data[4] = { r(), r(), r(), target + (r() % (std::numeric_limits<uint64_t>::max() - target + 1)) };
+			memcpy(h.h, data, HASH_SIZE);
+			EXPECT_EQ(diff.check_pow(h), false);
+		}
+	}
+}
+
+}
diff --git a/tests/src/tests.cpp b/tests/src/tests.cpp
new file mode 100644
index 0000000..2822d0c
--- /dev/null
+++ b/tests/src/tests.cpp
@@ -0,0 +1,24 @@
+/*
+ * This file is part of the Monero P2Pool <https://github.com/SChernykh/p2pool>
+ * Copyright (c) 2021 SChernykh <https://github.com/SChernykh>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "gtest/gtest.h"
+
+int main(int argc, char** argv)
+{
+	testing::InitGoogleTest(&argc, argv);
+	return RUN_ALL_TESTS();
+}