test(chat): 覆盖系统撤回/群名片/实时会话同步相关用例

- 新增系统撤回消息 replacemsg 解析与导出语义测试

- 新增群聊会话预览格式化与群名片 ext_buffer 解析测试

- 新增 realtime 会话列表与 sync_all 落库 last_sender_display_name 测试

tests/test_chat_session_preview_formatting.py

@@ -0,0 +1,68 @@
+import sqlite3
+import sys
+import unittest
+from pathlib import Path
+from tempfile import TemporaryDirectory
+
+
+ROOT = Path(__file__).resolve().parents[1]
+sys.path.insert(0, str(ROOT / "src"))
+
+from wechat_decrypt_tool.chat_helpers import (
+    _build_group_sender_display_name_map,
+    _normalize_session_preview_text,
+    _replace_preview_sender_prefix,
+)
+
+
+class TestChatSessionPreviewFormatting(unittest.TestCase):
+    def test_normalize_session_preview_emoji_label(self):
+        out = _normalize_session_preview_text("[表情]", is_group=False, sender_display_names={})
+        self.assertEqual(out, "[动画表情]")
+
+    def test_normalize_group_preview_sender_display_name(self):
+        out = _normalize_session_preview_text(
+            "wxid_u3gwceqvne2m22: [表情]",
+            is_group=True,
+            sender_display_names={"wxid_u3gwceqvne2m22": "食神"},
+        )
+        self.assertEqual(out, "食神: [动画表情]")
+
+    def test_build_group_sender_display_name_map_from_contact_db(self):
+        with TemporaryDirectory() as td:
+            contact_db_path = Path(td) / "contact.db"
+            conn = sqlite3.connect(str(contact_db_path))
+            try:
+                conn.execute(
+                    """
+                    CREATE TABLE contact (
+                        username TEXT,
+                        remark TEXT,
+                        nick_name TEXT,
+                        alias TEXT,
+                        big_head_url TEXT,
+                        small_head_url TEXT
+                    )
+                    """
+                )
+                conn.execute(
+                    "INSERT INTO contact VALUES (?, ?, ?, ?, ?, ?)",
+                    ("wxid_u3gwceqvne2m22", "", "食神", "", "", ""),
+                )
+                conn.commit()
+            finally:
+                conn.close()
+
+            mapping = _build_group_sender_display_name_map(
+                contact_db_path,
+                {"demo@chatroom": "wxid_u3gwceqvne2m22: [动画表情]"},
+            )
+            self.assertEqual(mapping.get("wxid_u3gwceqvne2m22"), "食神")
+
+    def test_replace_preview_sender_prefix_uses_group_nickname(self):
+        out = _replace_preview_sender_prefix("去码头整点🍟: [动画表情]", "麻辣香锅")
+        self.assertEqual(out, "麻辣香锅: [动画表情]")
+
+
+if __name__ == "__main__":
+    unittest.main()