diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
new file mode 100644
index 0000000..daa9d9b
--- /dev/null
+++ b/tests/CMakeLists.txt
@@ -0,0 +1,25 @@
+cmake_minimum_required(VERSION 3.10.0)
+project(test_plan_execute)
+include(FetchContent)
+if (MSVC)
+    add_compile_options(/utf-8)
+endif()
+FetchContent_Declare(
+  googletest
+  URL https://github.com/google/googletest/archive/03597a01ee50ed33e9dfd640b249b4be3799d395.zip
+)
+# For Windows: Prevent overriding the parent project's compiler/linker settings
+set(gtest_force_shared_crt ON CACHE BOOL "" FORCE)
+FetchContent_MakeAvailable(googletest)
+set(CMAKE_CXX_STANDARD 14)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+include_directories(${CMAKE_CURRENT_SOURCE_DIR}/../include)
+
+include(CTest)
+enable_testing()
+
+add_executable(test_plan_execute test_app.cpp ../src/app.cpp)
+
+target_link_libraries(test_plan_execute gtest gmock gtest_main)
+include(GoogleTest)
+gtest_discover_tests(test_plan_execute)
\ No newline at end of file
diff --git a/tests/test_app.cpp b/tests/test_app.cpp
new file mode 100644
index 0000000..65935da
--- /dev/null
+++ b/tests/test_app.cpp
@@ -0,0 +1,120 @@
+#include <gtest/gtest.h>
+#include "app.hpp"
+#include <fstream>
+#include <filesystem>
+
+namespace fs = std::filesystem;
+
+class TodoServiceTest : public ::testing::Test {
+protected:
+    void SetUp() override {
+        test_file_ = "test_todo.json";
+        if (fs::exists(test_file_)) fs::remove(test_file_);
+    }
+
+    void TearDown() override {
+        if (fs::exists(test_file_)) fs::remove(test_file_);
+    }
+
+    std::string test_file_;
+};
+
+TEST_F(TodoServiceTest, testLoadValidJsonFile) {
+    std::ofstream ofs(test_file_);
+    ofs << R"({
+      "items": [
+        {"id": 1, "title": "Task1", "description": "Desc1", "completed": false},
+        {"id": 2, "title": "Task2", "description": "Desc2", "completed": true}
+      ],
+      "next_id": 3
+    })";
+    ofs.close();
+
+    TodoService service(test_file_);
+    auto items = service.get_all();
+    ASSERT_EQ(items.size(), 2);
+    EXPECT_EQ(items[0].id, 1);
+    EXPECT_EQ(items[1].id, 2);
+    EXPECT_EQ(items[1].completed, true);
+
+    auto new_item = service.create("Task3", "Desc3");
+    EXPECT_EQ(new_item.id, 3);
+}
+
+TEST_F(TodoServiceTest, testLoadEmptyFile) {
+    std::ofstream ofs(test_file_);
+    ofs.close();
+
+    TodoService service(test_file_);
+    auto items = service.get_all();
+    EXPECT_TRUE(items.empty());
+
+    auto new_item = service.create("Task", "Desc");
+    EXPECT_EQ(new_item.id, 1);
+}
+
+TEST_F(TodoServiceTest, testLoadNonExistentFile) {
+    TodoService service("nonexistent.json");
+    auto items = service.get_all();
+    EXPECT_TRUE(items.empty());
+
+    auto new_item = service.create("Task", "Desc");
+    EXPECT_EQ(new_item.id, 1);
+}
+
+TEST_F(TodoServiceTest, testLoadInvalidJson) {
+    std::ofstream ofs(test_file_);
+    ofs << "invalid json content";
+    ofs.close();
+
+    TodoService service(test_file_);
+    auto items = service.get_all();
+    EXPECT_TRUE(items.empty());
+
+    auto new_item = service.create("Task", "Desc");
+    EXPECT_EQ(new_item.id, 1);
+}
+
+TEST_F(TodoServiceTest, testLoadNextIdAdjustment) {
+    std::ofstream ofs(test_file_);
+    ofs << R"({
+      "items": [
+        {"id": 5, "title": "Task", "description": "Desc", "completed": false}
+      ],
+      "next_id": 3
+    })";
+    ofs.close();
+
+    TodoService service(test_file_);
+    auto new_item = service.create("NewTask", "NewDesc");
+    EXPECT_EQ(new_item.id, 6);
+}
+
+TEST_F(TodoServiceTest, testSaveValidData) {
+    TodoService service(test_file_);
+    service.create("Task1", "Desc1");
+    service.create("Task2", "Desc2");
+
+    std::ifstream ifs(test_file_);
+    std::string content((std::istreambuf_iterator<char>(ifs)), std::istreambuf_iterator<char>());
+    EXPECT_NE(content.find("\"id\": 1"), std::string::npos);
+    EXPECT_NE(content.find("\"id\": 2"), std::string::npos);
+    EXPECT_NE(content.find("\"next_id\": 3"), std::string::npos);
+}
+
+TEST_F(TodoServiceTest, testSaveEmptyItems) {
+    TodoService service(test_file_);
+    auto item = service.create("Temp", "Desc");
+    service.delete_item(item.id);
+
+    std::ifstream ifs(test_file_);
+    std::string content((std::istreambuf_iterator<char>(ifs)), std::istreambuf_iterator<char>());
+    EXPECT_NE(content.find("\"items\": []"), std::string::npos);
+    EXPECT_NE(content.find("\"next_id\": 2"), std::string::npos);
+}
+
+TEST_F(TodoServiceTest, testSaveInvalidPath) {
+    TodoService service("/invalid/path/test.json");
+    EXPECT_NO_THROW(service.create("Task", "Desc"));
+    EXPECT_FALSE(fs::exists("/invalid/path/test.json"));
+}