diff --git a/src/core/common_code/sundry.cc b/src/core/common_code/sundry.cc
index d6976d8..d0eb320 100644
--- a/src/core/common_code/sundry.cc
+++ b/src/core/common_code/sundry.cc
@@ -52,6 +52,7 @@ CommonCode CommonCode::from_raw_code(RawCode raw_code) noexcept {
     return raw_code.to_common_code();
 }
 
+// TODO: using `std::optional::transform` in C++23
 std::optional<CommonCode> CommonCode::from_raw_code(uint64_t raw_code) noexcept {
     auto code = RawCode::create(raw_code);
     if (!code.has_value()) {
diff --git a/src/core_test/CMakeLists.txt b/src/core_test/CMakeLists.txt
index ddc13ee..90589e4 100644
--- a/src/core_test/CMakeLists.txt
+++ b/src/core_test/CMakeLists.txt
@@ -11,6 +11,9 @@ include_directories(utils)
 include_directories(${KLOTSKI_ROOT}/src/core/ffi)
 include_directories(${KLOTSKI_ROOT}/src/core/utils)
 include_directories(${KLOTSKI_ROOT}/src/core/all_cases)
+
+include_directories(${KLOTSKI_ROOT}/src/core/raw_code)
+include_directories(${KLOTSKI_ROOT}/src/core/short_code)
 include_directories(${KLOTSKI_ROOT}/src/core/common_code)
 
 ###############################################################################################
diff --git a/src/core_test/codec/common_code.cc b/src/core_test/codec/common_code.cc
index e69de29..69e37e5 100644
--- a/src/core_test/codec/common_code.cc
+++ b/src/core_test/codec/common_code.cc
@@ -0,0 +1,175 @@
+#include <algorithm>
+
+#include "all_cases.h"
+#include "raw_code.h"
+#include "short_code.h"
+#include "common_code.h"
+#include "gtest/gtest.h"
+#include "BS_thread_pool.hpp"
+
+using klotski::codec::RawCode;
+using klotski::codec::ShortCode;
+using klotski::codec::CommonCode;
+
+using klotski::cases::AllCases;
+using klotski::cases::ALL_CASES_NUM_;
+
+const static uint64_t TEST_CODE = 0x1'A9BF'0C00;
+const static std::string TEST_CODE_STR = "1A9BF0C00";
+
+TEST(CommonCode, validity) {
+    EXPECT_NE(CommonCode::check(0x3'A9'BF'0C'00), true); // invalid 2x2 block
+    EXPECT_NE(CommonCode::check(0x1'D9'BF'0C'00), true); // invalid block range
+    EXPECT_NE(CommonCode::check(0x1'A9'BF'FC'00), true); // less than 2 space
+    EXPECT_NE(CommonCode::check(0x1'A0'BF'0C'01), true); // low bits not fill zero
+
+    EXPECT_FALSE(CommonCode::create(0x123456789).has_value()); // invalid code
+    EXPECT_FALSE(CommonCode::from_string("0123456789").has_value()); // length > 9
+    EXPECT_FALSE(CommonCode::from_string("123J432A9").has_value()); // with invalid `J`
+}
+
+TEST(CommonCode, operators) {
+    auto common_code = CommonCode::create(TEST_CODE).value();
+
+    std::ostringstream tmp;
+    tmp << common_code; // ostream capture
+    EXPECT_EQ(tmp.str(), TEST_CODE_STR);
+    EXPECT_EQ((uint64_t)common_code, TEST_CODE); // convert as uint64_t
+
+    EXPECT_EQ(TEST_CODE, common_code); // uint64_t == CommonCode
+    EXPECT_EQ(common_code, TEST_CODE); // CommonCode == uint64_t
+    EXPECT_EQ(common_code, common_code); // CommonCode == CommonCode
+
+    EXPECT_NE(TEST_CODE + 1, common_code); // uint64_t != CommonCode
+    EXPECT_NE(common_code, TEST_CODE + 1); // CommonCode != uint64_t
+    EXPECT_NE(common_code, CommonCode::unsafe_create(TEST_CODE + 1)); // CommonCode != CommonCode
+
+    EXPECT_LT(common_code, CommonCode::unsafe_create(TEST_CODE + 1)); // CommonCode < CommonCode
+    EXPECT_GT(CommonCode::unsafe_create(TEST_CODE + 1), common_code); // CommonCode > CommonCode
+}
+
+TEST(CommonCode, code_verify) {
+    BS::thread_pool pool;
+    for (int head = 0; head < 16; ++head) {
+        pool.push_task([](uint64_t head) {
+            for (auto range : AllCases::instance().fetch()[head]) {
+                auto code = head << 32 | range;
+                EXPECT_TRUE(CommonCode::check(code)); // verify all valid code
+            }
+        }, head);
+    }
+    pool.wait_for_tasks();
+}
+
+TEST(CommonCode, code_string) {
+    auto test_func = [](CommonCode code) {
+        auto code_shorten = code.to_string(true); // with shorten
+        auto code_normal = code.to_string(false); // without shorten
+        EXPECT_TRUE(code_normal.starts_with(code_shorten));
+
+        EXPECT_LE(code_shorten.size(), 9); // length -> (0, 9]
+        EXPECT_NE(code_shorten.size(), 0);
+        if (code != 0) { // skip special code string `0`
+            EXPECT_NE(code_shorten.back(), '0');
+        }
+        EXPECT_EQ(CommonCode::from_string(code_shorten), code); // test upper cases
+        std::transform(code_shorten.begin(), code_shorten.end(), code_shorten.begin(), ::tolower);
+        EXPECT_EQ(CommonCode::from_string(code_shorten), code); // test lower cases
+
+        EXPECT_EQ(code_normal.size(), 9); // length = 9
+        for (auto c : code_normal) {
+            EXPECT_TRUE((c >= '0' && c <= '9') || (c >= 'A' && c <= 'F'));
+        }
+        EXPECT_EQ(CommonCode::from_string(code_normal), code); // test upper cases
+        std::transform(code_normal.begin(), code_normal.end(), code_normal.begin(), ::tolower);
+        EXPECT_EQ(CommonCode::from_string(code_normal), code); // test lower cases
+    };
+
+    BS::thread_pool pool;
+    for (int head = 0; head < 16; ++head) {
+        pool.push_task([&test_func](uint64_t head) {
+            for (auto range : AllCases::instance().fetch()[head]) {
+                test_func(CommonCode::unsafe_create(head << 32 | range));
+            }
+        }, head);
+    }
+    pool.wait_for_tasks();
+}
+
+TEST(CommonCode, code_convert) {
+    auto common_code = CommonCode::create(TEST_CODE).value();
+    EXPECT_EQ(common_code.unwrap(), TEST_CODE);
+    EXPECT_EQ(common_code.to_string(), TEST_CODE_STR);
+    EXPECT_EQ(common_code.to_raw_code(), RawCode(common_code));
+    EXPECT_EQ(common_code.to_short_code(), ShortCode(common_code));
+
+    auto code_shorten = common_code.to_string(true);
+    EXPECT_EQ(CommonCode::from_string(code_shorten), common_code); // l-value
+    EXPECT_EQ(CommonCode::from_string(std::move(code_shorten)), common_code); // r-value
+
+    auto code_normal = common_code.to_string(false);
+    EXPECT_EQ(CommonCode::from_string(code_normal), common_code); // l-value
+    EXPECT_EQ(CommonCode::from_string(std::move(code_normal)), common_code); // r-value
+}
+
+TEST(CommonCode, initializate) {
+    EXPECT_TRUE(CommonCode::create(TEST_CODE).has_value());
+    EXPECT_EQ(CommonCode::create(TEST_CODE), TEST_CODE);
+    EXPECT_EQ(CommonCode::unsafe_create(TEST_CODE), TEST_CODE);
+
+    auto common_code = CommonCode::create(TEST_CODE).value();
+    EXPECT_EQ(CommonCode(RawCode(common_code)), TEST_CODE);
+    EXPECT_EQ(CommonCode(ShortCode(common_code)), TEST_CODE);
+
+    EXPECT_TRUE(CommonCode::from_string(TEST_CODE_STR).has_value());
+    EXPECT_EQ(CommonCode::from_string(TEST_CODE_STR), TEST_CODE); // l-value
+    EXPECT_EQ(CommonCode::from_string(std::string(TEST_CODE_STR)), TEST_CODE); // r-value
+
+    auto raw_code = RawCode(common_code);
+    auto raw_code_val = raw_code.unwrap();
+    EXPECT_EQ(CommonCode::from_raw_code(raw_code), TEST_CODE);
+    EXPECT_TRUE(CommonCode::from_raw_code(raw_code_val).has_value());
+    EXPECT_EQ(CommonCode::from_raw_code(raw_code_val), TEST_CODE);
+
+    auto short_code = ShortCode(common_code);
+    auto short_code_val = short_code.unwrap();
+    auto short_code_str = short_code.to_string();
+    EXPECT_TRUE(CommonCode::from_short_code(short_code_val).has_value());
+    EXPECT_TRUE(CommonCode::from_short_code(short_code_str).has_value());
+    EXPECT_TRUE(CommonCode::from_short_code(std::string(short_code_str)).has_value());
+
+    EXPECT_EQ(CommonCode::from_short_code(short_code_val), TEST_CODE);
+    EXPECT_EQ(CommonCode::from_short_code(short_code), TEST_CODE);
+    EXPECT_EQ(CommonCode::from_short_code(short_code_str), TEST_CODE); // l-value
+    EXPECT_EQ(CommonCode::from_short_code(std::string(short_code_str)), TEST_CODE); // r-value
+}
+
+TEST(CommonCode, DISABLED_global) {
+    std::vector<uint64_t> common_codes;
+    common_codes.reserve(ALL_CASES_NUM_);
+    for (uint64_t head = 0; head < 16; ++head) {
+        for (auto range : AllCases::instance().fetch()[head]) {
+            common_codes.emplace_back(head << 32 | range);
+        }
+    }
+
+    BS::thread_pool pool;
+    auto futures = pool.parallelize_loop(0x10'0000'0000, [](uint64_t start, uint64_t end) {
+        std::vector<uint64_t> archive;
+        for (uint64_t common_code = start; common_code < end; ++common_code) { // brute-force search
+            if (CommonCode::check(common_code)) {
+                archive.emplace_back(common_code); // found valid common code
+            }
+        }
+        return archive;
+    }, 0x1000); // split as 4096 pieces
+
+    std::vector<uint64_t> result;
+    result.reserve(ALL_CASES_NUM_);
+    for (size_t i = 0; i < futures.size(); ++i) {
+        auto data = futures[i].get();
+        result.insert(result.end(), data.begin(), data.end()); // combine sections
+    }
+    pool.wait_for_tasks();
+    EXPECT_EQ(result, common_codes);
+}