diff --git a/ai_commons/file_processing/json_validator.py b/ai_commons/file_processing/json_validator.py
index 39cd288..caa7157 100644
--- a/ai_commons/file_processing/json_validator.py
+++ b/ai_commons/file_processing/json_validator.py
@@ -1,6 +1,7 @@
 # Json validator module
 
 import json
+from datetime import datetime
 
 def remove_keys_from_json(json_string, keys_to_remove):
     # 解析JSON字符串为列表
@@ -14,4 +15,31 @@ def remove_keys_from_json(json_string, keys_to_remove):
                     del data[key]
     
     # 将列表转换回JSON字符串
-    return json.dumps(data_list, ensure_ascii=False)
\ No newline at end of file
+    return json.dumps(data_list, ensure_ascii=False)
+
+import json
+from datetime import datetime
+
+def change_timestamp_format(json_string, timestamp_field):
+    """
+    将JSON字符串中的指定字段的时间戳格式从 'YYYY-MM-DD HH:MM:SS' 改为 'YYYY-MM-DD'。
+
+    Args:
+    json_string (str): 输入的JSON字符串。
+    timestamp_field (str): 需要转换时间戳格式的字段名。
+
+    Returns:
+    str: 修改后的JSON字符串。
+    """
+    data_list = json.loads(json_string)
+    
+    for data in data_list:
+        if timestamp_field in data:
+            try:
+                original_timestamp = data[timestamp_field]
+                new_timestamp = datetime.strptime(original_timestamp, '%Y-%m-%d %H:%M:%S').strftime('%Y-%m-%d')
+                data[timestamp_field] = new_timestamp
+            except ValueError:
+                pass
+    
+    return json.dumps(data_list, ensure_ascii=False)
diff --git a/tests/test_file_processing.py b/tests/test_file_processing.py
index 2b8f63e..61a2372 100644
--- a/tests/test_file_processing.py
+++ b/tests/test_file_processing.py
@@ -2,42 +2,70 @@
 import json
 import os
 import pandas as pd
+from datetime import datetime
 from ai_commons.file_processing.excel_parser import ExcelConverter
-from ai_commons.file_processing.json_validator import remove_keys_from_json
+from ai_commons.file_processing.json_validator import remove_keys_from_json, change_timestamp_format
 
 class TestExcelConverter(unittest.TestCase):
-
+    
     def setUp(self):
-        # 创建一个示例Excel文件
-        self.test_file = 'test.xlsx'
-        df = pd.DataFrame({
-            'Timestamp': [pd.Timestamp('2024-04-07 20:50:30'), pd.Timestamp('2024-05-08 15:30:45')],
-            'User ID': ['U12345', 'U67890'],
-            'Gift': ['Flower', 'Chocolate']
-        })
-        df.to_excel(self.test_file, index=False)
-
+        # 创建一个测试的DataFrame
+        self.data = {
+            'Timestamp': [pd.Timestamp('2024-04-20 22:03:30'), pd.Timestamp('2024-04-10 22:49:39')],
+            'Account': ['ABC123', 'XYZ789'],
+            'Holdback': ['None', 'Test holdback message'],
+            'Comments': [None, None],
+            'Features': [None, None]
+        }
+        self.df = pd.DataFrame(self.data)
+        
+        # 保存为Excel文件
+        self.test_excel_file = 'test_excel_file.xlsx'
+        self.df.to_excel(self.test_excel_file, index=False, engine='openpyxl')
+        
     def tearDown(self):
-        # 删除示例Excel文件
-        if os.path.exists(self.test_file):
-            os.remove(self.test_file)
+        # 删除测试文件
+        if os.path.exists(self.test_excel_file):
+            os.remove(self.test_excel_file)
 
-    def test_to_json(self):
-        converter = ExcelConverter(self.test_file)
-        json_output = converter.to_json(chunk_size=2)
-        expected_output = [
-            '[{"Timestamp": "2024-04-07 20:50:30", "User ID": "U12345", "Gift": "Flower"}, {"Timestamp": "2024-05-08 15:30:45", "User ID": "U67890", "Gift": "Chocolate"}]'
-        ]
-        self.assertEqual(json_output, expected_output)
+    def test_excel_to_json(self):
+        # 测试Excel转换为JSON
+        converter = ExcelConverter(self.test_excel_file)
+        json_string_list = converter.to_json(chunk_size=2)
+        
+        self.assertEqual(len(json_string_list), 1)
+        json_data = json.loads(json_string_list[0])
+        
+        self.assertEqual(len(json_data), 2)
+        self.assertEqual(json_data[0]['Account'], 'ABC123')
+        self.assertEqual(json_data[1]['Account'], 'XYZ789')
+        self.assertEqual(json_data[0]['Timestamp'], '2024-04-20 22:03:30')
 
 class TestJsonValidator(unittest.TestCase):
-
+    
+    def setUp(self):
+        self.json_string = '''
+        [
+            {"Timestamp": "2024-04-20 22:03:30", "Account": "ABC123", "Holdback": "None", "Comments": null, "Features": null},
+            {"Timestamp": "2024-04-10 22:49:39", "Account": "XYZ789", "Holdback": "Test holdback message", "Comments": null, "Features": null}
+        ]
+        '''
+    
     def test_remove_keys_from_json(self):
-        json_string = '[{"Timestamp": "2024-04-07 20:50:30", "User ID": "U12345", "Gift": "Flower"}, {"Timestamp": "2024-05-08 15:30:45", "User ID": "U67890", "Gift": "Chocolate"}]'
-        keys_to_remove = [["Timestamp"], ["User ID"]]
-        modified_json_string = remove_keys_from_json(json_string, keys_to_remove)
-        expected_output = '[{"Gift": "Flower"}, {"Gift": "Chocolate"}]'
-        self.assertEqual(modified_json_string, expected_output)
+        keys_to_remove = [["Comments"], ["Features"]]
+        cleaned_json_string = remove_keys_from_json(self.json_string, keys_to_remove)
+        cleaned_data = json.loads(cleaned_json_string)
+        
+        for item in cleaned_data:
+            self.assertNotIn("Comments", item)
+            self.assertNotIn("Features", item)
+    
+    def test_change_timestamp_format(self):
+        new_json_string = change_timestamp_format(self.json_string, "Timestamp")
+        new_data = json.loads(new_json_string)
+        
+        self.assertEqual(new_data[0]['Timestamp'], '2024-04-20')
+        self.assertEqual(new_data[1]['Timestamp'], '2024-04-10')
 
 if __name__ == '__main__':
     unittest.main()