diff --git a/src/core/include/scene/unit.hpp b/src/core/include/scene/unit.hpp
index 41ad459..8572961 100644
--- a/src/core/include/scene/unit.hpp
+++ b/src/core/include/scene/unit.hpp
@@ -220,9 +220,10 @@ namespace gkit::scene {
             using reference = Unit&;
 
         public:
+            // Constructor and operators
             iterator(Unit* owner, size_t pos);
-            auto operator*() -> reference const;
-            auto operator->() -> pointer const;
+            auto operator*() const -> reference;
+            auto operator->() const -> pointer;
             auto operator++() -> iterator&;
             auto operator++(int) -> iterator;
             auto operator--() -> iterator&;
@@ -236,10 +237,7 @@ namespace gkit::scene {
             friend class Unit;
         };
 
-        // Why this part didn't use auto, because it need to have a const_iterator use
-        // but auto could not allow two same function but with different return
-        // but begin() and end() need those two return
-        // So I will not change it
+
         auto begin() -> iterator;
         auto end() -> iterator;
 
@@ -253,9 +251,11 @@ namespace gkit::scene {
             using pointer = const Unit*;
             using reference = const Unit&;
 
+        public:
+            // Constructor and operators
             const_iterator(const Unit* owner, size_t pos);
-            auto operator*() -> reference const;
-            auto operator->() -> pointer const;
+            auto operator*() const -> reference;
+            auto operator->() const -> pointer;
             auto operator++() -> const_iterator&;
             auto operator++(int) -> const_iterator;
             auto operator--() -> const_iterator&;
diff --git a/src/core/scene/unit.cpp b/src/core/scene/unit.cpp
index 2c21eaa..539403f 100644
--- a/src/core/scene/unit.cpp
+++ b/src/core/scene/unit.cpp
@@ -188,11 +188,11 @@ auto gkit::scene::Unit::get_parent<gkit::scene::Unit>() noexcept -> std::optiona
 
 // iterator part use
 gkit::scene::Unit::iterator::iterator(Unit* owner, size_t pos) : m_owner(owner), m_pos(pos) {}
-auto gkit::scene::Unit::iterator::operator*() -> reference const {
+auto gkit::scene::Unit::iterator::operator*() const -> reference {
 auto child_opt = m_owner->get_available_child(static_cast<uint32_t>(m_pos));
     return **child_opt;
 }
-auto gkit::scene::Unit::iterator::operator->() -> pointer const {
+auto gkit::scene::Unit::iterator::operator->() const -> pointer {
     auto child_opt = m_owner->get_available_child(static_cast<uint32_t>(m_pos));
     return *child_opt;
 }
@@ -228,12 +228,12 @@ auto gkit::scene::Unit::end() -> iterator{
 // now is const_iterator use
 gkit::scene::Unit::const_iterator::const_iterator(const Unit* owner, size_t pos) : m_owner(owner), m_pos(pos) {}
 
-auto gkit::scene::Unit::const_iterator::operator*() -> reference const {
+auto gkit::scene::Unit::const_iterator::operator*() const -> reference {
     auto child_opt = const_cast<Unit*>(m_owner)->get_available_child(static_cast<uint32_t>(m_pos));
     return **child_opt;
 }
 
-auto gkit::scene::Unit::const_iterator::operator->() -> pointer const {
+auto gkit::scene::Unit::const_iterator::operator->() const -> pointer {
     auto child_opt = const_cast<Unit*>(m_owner)->get_available_child(static_cast<uint32_t>(m_pos));
     return *child_opt;
 }
@@ -274,8 +274,12 @@ auto gkit::scene::Unit::cbegin() const -> const_iterator { return begin(); }
 auto gkit::scene::Unit::cend() const -> const_iterator { return end(); }
 
 // This is a reverse iterator, implemented using std::reverse_iterator.
-using reverse_iterator = std::reverse_iterator<gkit::scene::Unit::iterator>;
-using const_reverse_iterator = std::reverse_iterator<gkit::scene::Unit::const_iterator>;
+// using at here maybe have some problem, just I guess,
+// So I deleted it
+
+// using reverse_iterator = std::reverse_iterator<gkit::scene::Unit::iterator>;
+// using const_reverse_iterator = std::reverse_iterator<gkit::scene::Unit::const_iterator>;
+
 auto gkit::scene::Unit::rbegin() -> reverse_iterator { return reverse_iterator(end()); }
 auto gkit::scene::Unit::rend() -> reverse_iterator { return reverse_iterator(begin()); }
 auto gkit::scene::Unit::rbegin() const -> const_reverse_iterator { return const_reverse_iterator(end()); }
diff --git a/test/core/scene/test_unit_iterator.cpp b/test/core/scene/test_unit_iterator.cpp
new file mode 100644
index 0000000..ff7eaba
--- /dev/null
+++ b/test/core/scene/test_unit_iterator.cpp
@@ -0,0 +1,120 @@
+#include "scene/unit.hpp"
+#include <gkit.hpp>
+#include <format>
+#include <iostream>
+#include <memory>
+#include <string>
+#include <vector>
+#include <iterator>
+
+using gkit::scene::Unit;
+
+#define TEST(cond, msg) do { \
+    if (!(cond)) { \
+        std::cerr << "FAIL: " << msg << " (" << __FILE__ << ":" << __LINE__ << ")" << std::endl; \
+        return false; \
+    } else { \
+        std::cout << "PASS: " << msg << std::endl; \
+    } \
+} while(0)
+
+
+class TestUnit : public Unit {
+public:
+    using Unit::ready_handler;
+    using Unit::process_handler;
+    using Unit::exit_handler;
+    using Unit::parent;
+
+    static auto create(std::string name = "") {
+        return Unit::create<TestUnit>(std::move(name));
+    }
+
+    int ready_calls = 0;
+    int process_calls = 0;
+    int physics_calls = 0;
+    int exit_calls = 0;
+    std::string name_storage;
+
+    // Custom constructor
+    TestUnit(const std::string& name) : Unit(name), name_storage(name) {}
+
+    void _ready() override {
+        ready_calls++;
+        std::cout << "TestUnit[" << name_storage << "] _ready()\n";
+    }
+    void _process() override {
+        process_calls++;
+        std::cout << "TestUnit[" << name_storage << "] _process()\n";
+    }
+    void _physics_process() override {
+        physics_calls++;
+    }
+    void _exit() override {
+        exit_calls++;
+        std::cout << "TestUnit[" << name_storage << "] _exit()\n";
+    }
+};
+
+// ==================== test ====================
+
+bool test_iterator() {
+    std::cout << "\n=== test_iterator ===\n";
+    auto parent = TestUnit::create("parent");
+    std::vector<TestUnit*> children;
+    for (int i = 0; i < 5; ++i) {
+        auto child = TestUnit::create("child" + std::to_string(i));
+        children.push_back(child.get());
+        parent->add_child(std::move(child));
+    }
+    parent->process_handler();
+
+    int idx = 0;
+    for (auto& u : *parent) {
+        TEST(&u == children[idx], "iterator order matches addition");
+        idx++;
+    }
+    TEST(idx == 5, "iterated all 5 children");
+
+    idx = 4;
+    for (auto it = parent->rbegin(); it != parent->rend(); ++it) {
+        TEST(&(*it) == children[idx], "reverse iterator order");
+        idx--;
+    }
+    TEST(idx == -1, "reverse iterated all");
+
+    auto it = parent->begin();
+    ++it;
+    TEST(&(*it) == children[1], "pre-increment");
+    auto old_it = it++;
+    TEST(&(*old_it) == children[1], "post-increment returns old value");
+    TEST(&(*it) == children[2], "post-increment advances iterator");
+    auto old_it2 = it--;
+    TEST(&(*old_it2) == children[2], "post-decrement returns old value");
+    TEST(&(*it) == children[1], "post-decrement moves iterator back");
+    --it;
+    TEST(&(*it) == children[0], "pre-decrement");
+
+    const auto& const_parent = *parent;
+    idx = 0;
+    for (auto& u : const_parent) {
+        TEST(&u == children[idx], "const iterator works");
+        idx++;
+    }
+    return true;
+}
+
+// ==================== main function ====================
+int main() {
+    bool all_passed = true;
+    // Only run iterator test
+    all_passed &= test_iterator();
+
+    if (all_passed) {
+        std::cout << "\nAll tests passed!\n";
+        return 0;
+    } else {
+        std::cerr << "\nSome tests failed.\n";
+        return 1;
+    }
+}
\ No newline at end of file