diff --git a/Makefile b/Makefile
index 6c468b6..e3ad8c6 100644
--- a/Makefile
+++ b/Makefile
@@ -1,18 +1,26 @@
-# executable files / archive files
+# executable files
 NAME			= push_swap
 CHECKER			= checker
 TEST_NAME		= unit_tester
+
+# libraries
 LIBFT			= $(LIBFT_DIR)/libft.a
 
 # compilar options
 CFLAGS			= -Werror -Wextra -Wall
 CXXFLAGS		= -std=c++17 -Wall -Wextra -Werror
 PROD_FLAGS		= -O3
-DEV_FLAGS		= -g -fsanitize=address,integer,undefined -O0 -D DEV
-LEAK_FLAGS		= -O0 -D DEV -D LEAK
+DEV_FLAGS		= -O0 -g -fsanitize=address,integer,undefined -D DEV
+LEAK_FLAGS		= -D LEAK
 DEPFLAGS		= -MMD -MP
 INCLUDE			= -I $(INC_DIR)
 
+# flag options
+# 1. PROD_FLAGS: flags for production
+# 2. DEV_FLAGS: flags for development
+# 3. LEAK_FLAGS: flags for checking leaks
+FLAGS_OPTION	= $(PROD_FLAGS)
+
 # directories
 SRC_DIR			= src
 BUILD_DIR		= build
@@ -55,6 +63,7 @@ OBJ_FILTER_MAIN	= $(filter-out $(BUILD_DIR)/main.o, $(patsubst $(SRC_DIR)/%.c, $
 
 # bonus source files
 BONUS_SRC		= $(SRC_DIR)/checker/checker_main.c \
+					$(SRC_DIR)/checker/sort_based_on_operation.c \
 					$(SRC_DIR)/initialization/check_args.c \
 					$(SRC_DIR)/initialization/exit_with_error.c \
 					$(SRC_DIR)/initialization/generate_stack.c \
@@ -64,10 +73,14 @@ BONUS_SRC		= $(SRC_DIR)/checker/checker_main.c \
 					$(SRC_DIR)/stack_operations/rotate.c \
 					$(SRC_DIR)/stack_operations/reverse_rotate.c \
 					$(SRC_DIR)/utils/get_content.c \
-					$(SRC_DIR)/utils/stack_size.c
+					$(SRC_DIR)/utils/stack_size.c \
+					$(SRC_DIR)/utils/clear_stack.c
 BONUS_OBJ		= $(patsubst $(SRC_DIR)/%.c, $(BUILD_DIR)/%.o, $(BONUS_SRC))
 BONUS_DEP		= $(patsubst $(SRC_DIR)/%.c, $(BUILD_DIR)/%.d, $(BONUS_SRC))
 
+# header files
+HEADER			= $(wildcard $(INC_DIR)/*.h)
+
 # test files
 TEST_SRC		= $(TEST_DIR)/test_check_args.cpp \
 					$(TEST_DIR)/test_push_stack.cpp \
@@ -85,11 +98,11 @@ TEST_OBJ		= $(patsubst $(TEST_DIR)/%.cpp, $(TEST_BUILD_DIR)/%.o, $(TEST_SRC))
 GTEST_SRC		= $(GTEST_DIR)/gtest_main.cc $(GTEST_DIR)/gtest-all.cc
 GTEST_OBJ		= $(patsubst $(GTEST_DIR)/%.cc, $(TEST_BUILD_DIR)/%.o, $(GTEST_SRC))
 
-GTEST_VERSION	= 1.14.0
-GTEST_ARCHIVE	= v$(GTEST_VERSION).tar.gz
-GTEST_REPO_URL	= https://github.com/google/googletest/archive/refs/tags/$(GTEST_ARCHIVE)
-GTEST_SRC_DIR	= googletest-$(GTEST_VERSION)
-GTEST_FUSE_URL	= https://raw.githubusercontent.com/google/googletest/ec44c6c1675c25b9827aacd08c02433cccde7780/googletest/scripts/$(GTEST_FUSE)
+# google test version: 1.14.0
+GTEST_ARCHIVE	= v1.14.0.tar.gz
+GTEST_REPO_URL	= https://github.com/google/googletest/archive/refs/tags/v1.14.0.tar.gz
+GTEST_SRC_DIR	= googletest-1.14.0
+GTEST_FUSE_URL	= https://raw.githubusercontent.com/google/googletest/ec44c6c1675c25b9827aacd08c02433cccde7780/googletest/scripts/fuse_gtest_files.py
 GTEST_FUSE		= fuse_gtest_files.py
 
 # colors
@@ -104,37 +117,38 @@ MAGENTA			= \033[0;95m
 CYAN			= \033[0;96m
 WHITE			= \033[0;97m
 
-# flags options
-# 1. PROD_FLAGS: flags for production
-# 2. DEV_FLAGS: flags for development
-# 3. LEAK_FLAGS: flangs for checking leaks
-
 # rules for mandatory
-all: CFLAGS += $(PROD_FLAGS)
+.PHONY: all
+all: CFLAGS += $(FLAGS_OPTION)
 all: $(NAME)
 
-$(NAME): $(LIBFT) $(SRC)
-	@make _main
+$(NAME): $(LIBFT) $(SRC) $(HEADER)
+	@make _main CFLAGS="$(CFLAGS)"
 
+.PHONY: _main
 _main:
 	@echo "$(BLUE)[$(NAME)]\t./$(NAME)$(RESET)\t$(WHITE)compling...$(RESET)"
-	@make _build
+	@make _build CFLAGS="$(CFLAGS)"
 
+.PHONY: _build
 _build: $(OBJ)
 	@$(CC) $(CFLAGS) $^ -L $(LIBFT_DIR) -lft -o $(NAME)
 	@echo "\n$(BLUE)[$(NAME)]\t./$(NAME)$(RESET)\t$(GREEN)compiled ✔$(RESET)"
 
 # rules for bonus
-bonus: CFLAGS += $(PROD_FLAGS)
+.PHONY: bonus
+bonus: CFLAGS += $(FLAGS_OPTION)
 bonus: $(CHECKER)
 
-$(CHECKER): $(LIBFT) $(BONUS_SRC)
-	@make _checker_main
+$(CHECKER): $(LIBFT) $(BONUS_SRC) $(HEADER)
+	@make _checker_main CFLAGS="$(CFLAGS)"
 
+.PHONY: _checker_main
 _checker_main:
 	@echo "$(BLUE)[$(CHECKER)]\t./$(CHECKER)$(RESET)\t$(WHITE)compling...$(RESET)"
-	@make _checker_build
+	@make _checker_build CFLAGS="$(CFLAGS)"
 
+.PHONY: _checker_build
 _checker_build: $(BONUS_OBJ)
 	@$(CC) $(CFLAGS) $^ -L $(LIBFT_DIR) -lft -o $(CHECKER)
 	@echo "\n$(BLUE)[$(CHECKER)]\t./$(CHECKER)$(RESET)\t$(GREEN)compiled ✔$(RESET)"
@@ -145,9 +159,13 @@ $(BUILD_DIR)/%.o: $(SRC_DIR)/%.c
 	@$(CC) $(CFLAGS) $(INCLUDE) $(DEPFLAGS) -c $< -o $@
 	@printf "$(GREEN)─$(RESET)"
 
-$(LIBFT):
+$(LIBFT): $(LIBFT_DIR)
 	@make -C $(@D)
 
+$(LIBFT_DIR):
+	@git submodule update --init
+
+.PHONY: clean
 clean:
 	@make clean -C $(LIBFT_DIR)
 	@$(RM) $(OBJ) $(DEP)
@@ -155,6 +173,7 @@ clean:
 	@$(RM) $(BONUS_OBJ) $(BONUS_DEP)
 	@echo "$(BLUE)[$(CHECKER)]\tobject files$(RESET)\t$(GREEN)deleted ✔$(RESET)"
 
+.PHONY: fclean
 fclean: clean
 	@make fclean -C $(LIBFT_DIR)
 	@$(RM) $(NAME)
@@ -162,32 +181,36 @@ fclean: clean
 	@$(RM) $(CHECKER)
 	@echo "$(BLUE)[$(CHECKER)]\t./$(NAME)$(RESET)\t$(GREEN)deleted ✔$(RESET)"
 
+.PHONY: re
 re: fclean all
 
 # rules for test
+.PHONY: test
 test: all $(GTEST_OBJ) $(TEST_OBJ)
-	@echo "$(BLUE)\ntest linking$(RESET)"
 	@$(CXX) -L $(LIBFT_DIR) -lft -lpthread $(OBJ_FILTER_MAIN) $(TEST_OBJ) $(GTEST_OBJ) -o $(TEST_NAME)
+	@echo "\n$(BLUE)[gtest]\t\t./$(TEST_NAME)$(RESET)\t$(GREEN)compiled ✔$(RESET)"
 	./$(TEST_NAME)
 
+.PHONY: test_clean
 test_clean:
-	@echo "$(BLUE)test cleaning$(RESET)"
 	@$(RM) -r $(TEST_BUILD_DIR)
+	@echo "$(BLUE)[gtest]\t\t./$(TEST_NAME)$(RESET)\t$(GREEN)deleted ✔$(RESET)"
 
+.PHONY: retest
 retest: test_clean test
 
 $(TEST_BUILD_DIR)/%.o: $(TEST_DIR)/%.cpp
 	@mkdir -p $(@D)
 	@$(CXX) $(CXXFLAGS) -I $(TEST_DIR) $(INCLUDE) -c $< -o $@
-	@printf "$(GREEN).$(RESET)"
+	@printf "$(GREEN)─$(RESET)"
 
 $(GTEST_OBJ): $(GTEST_DIR)
-	@echo "$(BLUE)test compiling$(RESET)"
+	@echo "$(BLUE)[gtest]\t\t./$(TEST_NAME)$(RESET)\t$(WHITE)compling...$(RESET)"
 	@mkdir -p $(@D)
 	@$(CXX) $(CXXFLAGS) -I $(TEST_DIR) $(INCLUDE) -c $(GTEST_DIR)/gtest-all.cc -o $(TEST_BUILD_DIR)/gtest-all.o
-	@printf "$(GREEN).$(RESET)"
+	@printf "$(GREEN)─$(RESET)"
 	@$(CXX) $(CXXFLAGS) -I $(TEST_DIR) $(INCLUDE) -c $(GTEST_DIR)/gtest_main.cc -o $(TEST_BUILD_DIR)/gtest_main.o
-	@printf "$(GREEN).$(RESET)"
+	@printf "$(GREEN)─$(RESET)"
 
 $(GTEST_DIR):
 	@echo "fetching google test"
@@ -200,9 +223,8 @@ $(GTEST_DIR):
 	@mv $(GTEST_DIR)/gtest/* $(GTEST_DIR)
 	@$(RM) -r $(GTEST_SRC_DIR) $(GTEST_DIR)/gtest $(GTEST_ARCHIVE) $(GTEST_FUSE)
 
+.PHONY: norm
 norm:
 	norminette $(INC_DIR) $(SRC_DIR) $(LIBFT_DIR)
 
-.PHONY: all clean fclean re dev redev leak releak test norm title
-
 -include $(DEP)
diff --git a/include/checker.h b/include/checker.h
index 710cc51..a284326 100644
--- a/include/checker.h
+++ b/include/checker.h
@@ -6,7 +6,7 @@
 /*   By: reasuke <reasuke@student.42tokyo.jp>       +#+  +:+       +#+        */
 /*                                                +#+#+#+#+#+   +#+           */
 /*   Created: 2024/02/14 10:26:54 by reasuke           #+#    #+#             */
-/*   Updated: 2024/02/14 10:29:44 by reasuke          ###   ########.fr       */
+/*   Updated: 2024/02/19 12:11:08 by reasuke          ###   ########.fr       */
 /*                                                                            */
 /* ************************************************************************** */
 
@@ -16,4 +16,6 @@
 # include "../libft/libft.h"
 # include "types.h"
 
+void	sort_based_on_operation(t_stack **p_a, t_stack **p_b);
+
 #endif
diff --git a/src/checker/checker_main.c b/src/checker/checker_main.c
index dab9669..9235b5f 100644
--- a/src/checker/checker_main.c
+++ b/src/checker/checker_main.c
@@ -6,73 +6,34 @@
 /*   By: reasuke <reasuke@student.42tokyo.jp>       +#+  +:+       +#+        */
 /*                                                +#+#+#+#+#+   +#+           */
 /*   Created: 2024/02/14 10:25:27 by reasuke           #+#    #+#             */
-/*   Updated: 2024/02/14 13:50:38 by reasuke          ###   ########.fr       */
+/*   Updated: 2024/02/19 12:49:49 by reasuke          ###   ########.fr       */
 /*                                                                            */
 /* ************************************************************************** */
 
 #include "checker.h"
 #include "initialization.h"
 #include "sort.h"
-#include "stack_operations.h"
 
-static bool	_is_operation_present(const char *op)
-{
-	bool	present;
+#ifdef LEAK
+# ifdef __APPLE__
 
-	present = false;
-	present |= !ft_strcmp(op, "sa\n");
-	present |= !ft_strcmp(op, "sb\n");
-	present |= !ft_strcmp(op, "ss\n");
-	present |= !ft_strcmp(op, "pa\n");
-	present |= !ft_strcmp(op, "pb\n");
-	present |= !ft_strcmp(op, "ra\n");
-	present |= !ft_strcmp(op, "rb\n");
-	present |= !ft_strcmp(op, "rr\n");
-	present |= !ft_strcmp(op, "rra\n");
-	present |= !ft_strcmp(op, "rrb\n");
-	present |= !ft_strcmp(op, "rrr\n");
-	return (present);
-}
+void		leak_check(void) __attribute__((destructor));
 
-static void	_stack_operation(t_stack **p_a, t_stack **p_b, const char *op)
+void	leak_check(void)
 {
-	if (!ft_strcmp(op, "sa\n") || !ft_strcmp(op, "ss\n"))
-		swap_stack(p_a);
-	if (!ft_strcmp(op, "sb\n") || !ft_strcmp(op, "ss\n"))
-		swap_stack(p_b);
-	if (!ft_strcmp(op, "pa\n"))
-		push_stack(p_b, p_a);
-	if (!ft_strcmp(op, "pb\n"))
-		push_stack(p_a, p_b);
-	if (!ft_strcmp(op, "ra\n") || !ft_strcmp(op, "rr\n"))
-		rotate_stack(p_a);
-	if (!ft_strcmp(op, "rb\n") || !ft_strcmp(op, "rr\n"))
-		rotate_stack(p_b);
-	if (!ft_strcmp(op, "rra\n") || !ft_strcmp(op, "rrr\n"))
-		reverse_rotate_stack(p_a);
-	if (!ft_strcmp(op, "rrb\n") || !ft_strcmp(op, "rrr\n"))
-		reverse_rotate_stack(p_b);
+	system("leaks -q checker");
 }
 
-static void	_sort_based_on_operation(t_stack **p_a, t_stack **p_b)
-{
-	char	*op;
-
-	while (true)
-	{
-		op = get_next_line(STDIN_FILENO);
-		if (!op)
-			break ;
-		if (!_is_operation_present(op))
-			exit_with_error();
-		_stack_operation(p_a, p_b, op);
-	}
-}
+# endif
+#endif
 
 static void	_check_sorted(t_stack *st_a, int size_a)
 {
 	if (stack_size(st_a) != size_a)
+	{
 		ft_putendl_fd("KO", STDOUT_FILENO);
+		return ;
+	}
 	if (is_sorted_stack(st_a))
 		ft_putendl_fd("OK", STDOUT_FILENO);
 	else
@@ -89,7 +50,9 @@ int	main(int argc, char **argv)
 	check_args(argc, argv);
 	st_a = generate_stack(argc, argv);
 	st_b = NULL;
-	_sort_based_on_operation(&st_a, &st_b);
+	sort_based_on_operation(&st_a, &st_b);
 	_check_sorted(st_a, argc - 1);
+	clear_stack(&st_a, free);
+	clear_stack(&st_b, free);
 	return (0);
 }
diff --git a/src/checker/sort_based_on_operation.c b/src/checker/sort_based_on_operation.c
new file mode 100644
index 0000000..eaab9b2
--- /dev/null
+++ b/src/checker/sort_based_on_operation.c
@@ -0,0 +1,70 @@
+/* ************************************************************************** */
+/*                                                                            */
+/*                                                        :::      ::::::::   */
+/*   sort_based_on_operation.c                          :+:      :+:    :+:   */
+/*                                                    +:+ +:+         +:+     */
+/*   By: reasuke <reasuke@student.42tokyo.jp>       +#+  +:+       +#+        */
+/*                                                +#+#+#+#+#+   +#+           */
+/*   Created: 2024/02/19 12:10:41 by reasuke           #+#    #+#             */
+/*   Updated: 2024/02/19 12:48:45 by reasuke          ###   ########.fr       */
+/*                                                                            */
+/* ************************************************************************** */
+
+#include "checker.h"
+#include "initialization.h"
+#include "stack_operations.h"
+
+static bool	_is_operation_present(const char *op)
+{
+	bool	present;
+
+	present = false;
+	present |= !ft_strcmp(op, "sa\n");
+	present |= !ft_strcmp(op, "sb\n");
+	present |= !ft_strcmp(op, "ss\n");
+	present |= !ft_strcmp(op, "pa\n");
+	present |= !ft_strcmp(op, "pb\n");
+	present |= !ft_strcmp(op, "ra\n");
+	present |= !ft_strcmp(op, "rb\n");
+	present |= !ft_strcmp(op, "rr\n");
+	present |= !ft_strcmp(op, "rra\n");
+	present |= !ft_strcmp(op, "rrb\n");
+	present |= !ft_strcmp(op, "rrr\n");
+	return (present);
+}
+
+static void	_stack_operation(t_stack **p_a, t_stack **p_b, const char *op)
+{
+	if (!ft_strcmp(op, "sa\n") || !ft_strcmp(op, "ss\n"))
+		swap_stack(p_a);
+	if (!ft_strcmp(op, "sb\n") || !ft_strcmp(op, "ss\n"))
+		swap_stack(p_b);
+	if (!ft_strcmp(op, "pa\n"))
+		push_stack(p_b, p_a);
+	if (!ft_strcmp(op, "pb\n"))
+		push_stack(p_a, p_b);
+	if (!ft_strcmp(op, "ra\n") || !ft_strcmp(op, "rr\n"))
+		rotate_stack(p_a);
+	if (!ft_strcmp(op, "rb\n") || !ft_strcmp(op, "rr\n"))
+		rotate_stack(p_b);
+	if (!ft_strcmp(op, "rra\n") || !ft_strcmp(op, "rrr\n"))
+		reverse_rotate_stack(p_a);
+	if (!ft_strcmp(op, "rrb\n") || !ft_strcmp(op, "rrr\n"))
+		reverse_rotate_stack(p_b);
+}
+
+void	sort_based_on_operation(t_stack **p_a, t_stack **p_b)
+{
+	char	*op;
+
+	while (true)
+	{
+		op = get_next_line(STDIN_FILENO);
+		if (!op)
+			break ;
+		if (!_is_operation_present(op))
+			exit_with_error();
+		_stack_operation(p_a, p_b, op);
+		free(op);
+	}
+}
diff --git a/src/initialization/check_args.c b/src/initialization/check_args.c
index 544e5a3..6d5ca31 100644
--- a/src/initialization/check_args.c
+++ b/src/initialization/check_args.c
@@ -6,7 +6,7 @@
 /*   By: reasuke <reasuke@student.42tokyo.jp>       +#+  +:+       +#+        */
 /*                                                +#+#+#+#+#+   +#+           */
 /*   Created: 2024/01/11 14:44:55 by reasuke           #+#    #+#             */
-/*   Updated: 2024/02/13 11:45:54 by reasuke          ###   ########.fr       */
+/*   Updated: 2024/02/19 12:56:30 by reasuke          ###   ########.fr       */
 /*                                                                            */
 /* ************************************************************************** */
 
@@ -67,6 +67,8 @@ static bool	_has_duplicate(int argc, char **argv)
 
 int	check_args(int argc, char **argv)
 {
+	if (argc == 1)
+		exit(0);
 	if (_has_not_digit(argc, argv) || _has_overflow(argc, argv)
 		|| _has_duplicate(argc, argv))
 		exit_with_error();
diff --git a/src/main.c b/src/main.c
index f11c1b7..2894ed0 100644
--- a/src/main.c
+++ b/src/main.c
@@ -6,7 +6,7 @@
 /*   By: reasuke <reasuke@student.42tokyo.jp>       +#+  +:+       +#+        */
 /*                                                +#+#+#+#+#+   +#+           */
 /*   Created: 2024/01/10 12:37:36 by reasuke           #+#    #+#             */
-/*   Updated: 2024/02/13 22:58:00 by reasuke          ###   ########.fr       */
+/*   Updated: 2024/02/19 12:06:15 by reasuke          ###   ########.fr       */
 /*                                                                            */
 /* ************************************************************************** */
 
@@ -15,22 +15,14 @@
 #ifdef LEAK
 # ifdef __APPLE__
 
-void	leak_chek(void) __attribute__((destructor));
+void	leak_check(void) __attribute__((destructor));
 
-void	leak_chek(void)
+void	leak_check(void)
 {
 	system("leaks -q push_swap");
 }
 
 # endif
-#endif
-#ifdef DEV
-
-void	put_void(void *content)
-{
-	ft_printf("%d\n", *(int *)content);
-}
-
 #endif
 
 int	main(int argc, char **argv)
diff --git a/test/e2e/spec/checker_spec.rb b/test/e2e/spec/checker_spec.rb
index b9f6945..4ba8c5e 100644
--- a/test/e2e/spec/checker_spec.rb
+++ b/test/e2e/spec/checker_spec.rb
@@ -3,13 +3,11 @@
 require_relative "../helper/command_helper"
 
 describe("Performance test for push_swap") do
-  [5, 10, 50, 100, 200, 500, 1000].each do |size|
+  [1, 2, 3, 4, 5, 10, 50, 100, 200, 500, 1000].each do |size|
     it "measures operations for random input of size #{size}" do
-      results = []
-      input = (0...size).to_a.shuffle.map(&:to_s)
-      stdout, _stderr, status = execute_push_swap(*input)
+      input = (-10000..10000).to_a.sample(size).map(&:to_s)
+      _stdout, _stderr, status = execute_push_swap(*input)
       expect(status.exitstatus).to(eq(0))
-      results << stdout.split("\n").count
 
       stdout, _stderr, status = execute_checker(*input)
       expect(status.exitstatus).to(eq(0))
diff --git a/test/e2e/spec/corner_cases_spec.rb b/test/e2e/spec/corner_cases_spec.rb
index f1111da..71eda60 100644
--- a/test/e2e/spec/corner_cases_spec.rb
+++ b/test/e2e/spec/corner_cases_spec.rb
@@ -3,6 +3,13 @@
 require_relative "../helper/command_helper"
 
 describe "Corner cases for push_swap" do
+  it "does not output anything for not inputs" do
+    stdout, _stderr, status = execute_push_swap
+
+    expect(stdout).to(eq(""))
+    expect(status.exitstatus).to(eq(0))
+  end
+
   it "does not output operations for already sorted input" do
     stdout, _stderr, status = execute_push_swap("0", "1", "2", "3")
     expect(stdout).to(eq(""))
diff --git a/test/e2e/spec/error_cases_spec.rb b/test/e2e/spec/error_cases_spec.rb
index e63d4bd..363ccbf 100644
--- a/test/e2e/spec/error_cases_spec.rb
+++ b/test/e2e/spec/error_cases_spec.rb
@@ -3,21 +3,39 @@
 require_relative "../helper/command_helper"
 
 describe "Error cases for push_swap" do
-  it "returns error for non integer inputs" do
-    _stdout, stderr, status = execute_push_swap("a", "b", "c")
+  describe "when inputs are not integers" do
+    it "reports an error if all arguments are non-integer" do
+      _stdout, stderr, status = execute_push_swap("a", "b", "c")
 
-    expect(stderr).to(eq("Error\n"))
-    expect(status.exitstatus).to(eq(1))
+      expect(stderr).to(eq("Error\n"))
+      expect(status.exitstatus).to(eq(1))
+    end
+
+    it "reports an error if any argument is non-integer" do
+      _stdout, stderr, status = execute_push_swap("3", "push_swap", "5", "4", "1", "0", "2")
+
+      expect(stderr).to(eq("Error\n"))
+      expect(status.exitstatus).to(eq(1))
+    end
   end
 
-  it "returns error for duplicates" do
-    _stdout, stderr, status = execute_push_swap("3", "2", "5", "4", "1", "0", "2")
+  describe "when there are duplicate inputs" do
+    it "reports an error if all arguments are the same" do
+      _stdout, stderr, status = execute_push_swap("3", "3", "3", "3", "3", "3", "3")
 
-    expect(stderr).to(eq("Error\n"))
-    expect(status.exitstatus).to(eq(1))
+      expect(stderr).to(eq("Error\n"))
+      expect(status.exitstatus).to(eq(1))
+    end
+
+    it "reports an error if there are any duplicate arguments" do
+      _stdout, stderr, status = execute_push_swap("3", "2", "5", "4", "1", "0", "2")
+
+      expect(stderr).to(eq("Error\n"))
+      expect(status.exitstatus).to(eq(1))
+    end
   end
 
-  it "returns error for overflow" do
+  it "reports an error for integer overflow" do
     _stdout, stderr, status = execute_push_swap("0", "3", "2", "34578347984", "1")
 
     expect(stderr).to(eq("Error\n"))
diff --git a/test/unit/test_is_sorted_stack.cpp b/test/unit/test_is_sorted_stack.cpp
index f77a9df..1f1c63e 100644
--- a/test/unit/test_is_sorted_stack.cpp
+++ b/test/unit/test_is_sorted_stack.cpp
@@ -10,6 +10,14 @@ extern "C" {
 #include "sort.h"
 }
 
+TEST(is_sorted_stack, oneElement) {
+  t_stack *st;
+  t_content *c = new t_content({0, -1, 0, 0, 0, 0, 0, INIT, false});
+
+  st = ft_lstnew(c);
+  EXPECT_TRUE(is_sorted_stack(st));
+}
+
 // st: sorted
 // 0
 // 1