diff --git a/src/core/core/core.h b/src/core/core/core.h
index a085e44..5b00299 100644
--- a/src/core/core/core.h
+++ b/src/core/core/core.h
@@ -63,6 +63,10 @@
 
 namespace klotski::core {
 
+// TODO: new version without mask
+
+// TODO: allow wrap as a function directly
+
 class Core {
 public:
     /// Release with code and mask
diff --git a/src/core_test/core/core.cc b/src/core_test/core/core.cc
index db0052a..3419aa0 100644
--- a/src/core_test/core/core.cc
+++ b/src/core_test/core/core.cc
@@ -4,6 +4,8 @@
 
 #include <unordered_set>
 
+#include "utils/common.h"
+
 #include "all_cases/all_cases.h"
 #include "common_code/common_code.h"
 
@@ -11,7 +13,7 @@ using klotski::core::Core;
 using klotski::cases::AllCases;
 using klotski::codec::CommonCode;
 
-// mask test
+using klotski::codec::RawCode;
 
 TEST(core, core) {
 
@@ -49,3 +51,120 @@ TEST(core, core) {
     // std::cout << codes.size() << std::endl;
 
 }
+
+// TODO: support multi-thread test
+
+TEST(core, mask) {
+    std::vector<uint64_t> raw_codes;
+    raw_codes.reserve(klotski::cases::ALL_CASES_NUM_);
+
+    for (uint64_t head = 0; head < 16; ++head) {
+        for (const auto range : AllCases::instance().fetch()[head]) {
+            auto common_code = CommonCode::unsafe_create(head << 32 | range);
+            auto raw_code = common_code.to_raw_code().unwrap();
+            raw_codes.emplace_back(raw_code);
+        }
+    }
+
+    uint64_t src;
+
+    auto core = Core([&src](uint64_t ret, uint64_t mask) {
+
+        EXPECT_EQ(std::popcount(mask), 3);
+
+        auto num = std::countr_zero(mask);
+
+        uint64_t full_mask;
+
+        switch ((ret >> num) & 0b111) {
+        case BLOCK_1x1:
+            full_mask = K_MASK_1x1_ << num;
+            break;
+        case BLOCK_1x2:
+            full_mask = K_MASK_1x2_ << num;
+            break;
+        case BLOCK_2x1:
+            full_mask = K_MASK_2x1_ << num;
+            break;
+        case BLOCK_2x2:
+            full_mask = K_MASK_2x2_ << num;
+            break;
+        default:
+            EXPECT_TRUE(false);
+            return;
+        }
+
+        auto removed = ret & ~full_mask;
+
+        auto moved = (ret & full_mask) >> num;
+
+        switch ((ret >> num) & 0b111) {
+        case BLOCK_1x1:
+            EXPECT_EQ(moved, K_MASK_1x1);
+            break;
+        case BLOCK_1x2:
+            EXPECT_EQ(moved, K_MASK_1x2);
+            break;
+        case BLOCK_2x1:
+            EXPECT_EQ(moved, K_MASK_2x1);
+            break;
+        case BLOCK_2x2:
+            EXPECT_EQ(moved, K_MASK_2x2);
+            break;
+        default:
+            EXPECT_TRUE(false);
+            return;
+        }
+
+//        std::cout << RawCode::unsafe_create(full_mask) << std::endl;
+//        std::cout << RawCode::unsafe_create(ret) << std::endl;
+//        std::cout << RawCode::unsafe_create(removed) << std::endl;
+
+        auto diff = src ^ removed;
+//        std::cout << RawCode::unsafe_create(diff) << std::endl;
+//        std::cout << RawCode::unsafe_create(moved) << std::endl;
+
+        int tmp;
+        switch ((ret >> num) & 0b111) {
+        case BLOCK_1x1:
+            tmp = std::countr_zero(diff) - 0;
+            EXPECT_EQ(diff >> tmp, moved);
+            break;
+        case BLOCK_1x2:
+            tmp = std::countr_zero(diff) - 0;
+            EXPECT_EQ(diff >> tmp, moved);
+            break;
+        case BLOCK_2x1:
+            tmp = std::countr_zero(diff) - 1;
+            EXPECT_EQ(diff >> tmp, moved);
+            break;
+        case BLOCK_2x2:
+            tmp = std::countr_zero(diff) - 2;
+            EXPECT_EQ(diff >> tmp, moved);
+            break;
+        default:
+            EXPECT_TRUE(false);
+            return;
+        }
+
+//        std::cout << "----------------" << std::endl;
+
+//        EXPECT_NE(src, ret);
+
+    });
+
+    for (auto raw_code : raw_codes) {
+
+        src = raw_code;
+
+        core.next_cases(raw_code, 0);
+    }
+
+
+//    auto raw_code = RawCode::from_common_code(0x1A9BF0C00).value();
+//    auto raw_code = RawCode::from_common_code(0x4FEA13400).value();
+//    src = raw_code.unwrap();
+//
+//    core.next_cases(raw_code.unwrap(), 0);
+
+}