feat: Add Excel export functionality and unit tests

Features:
- Excel export with formatted multi-sheet workbooks (Contents, Comments, Creators)
- Professional styling: blue headers, auto-width columns, borders, text wrapping
- Smart export: empty sheets automatically removed
- Support for all platforms (xhs, dy, ks, bili, wb, tieba, zhihu)

Testing:
- Added pytest framework with asyncio support
- Unit tests for Excel store functionality
- Unit tests for store factory pattern
- Shared fixtures for test data
- Test coverage for edge cases

Documentation:
- Comprehensive Excel export guide (docs/excel_export_guide.md)
- Updated README.md and README_en.md with Excel examples
- Updated config comments to include excel option

Dependencies:
- Added openpyxl>=3.1.2 for Excel support
- Added pytest>=7.4.0 and pytest-asyncio>=0.21.0 for testing

This contribution adds immediate value for users who need data analysis
capabilities and establishes a testing foundation for future development.

tests/test_store_factory.py

@@ -0,0 +1,75 @@
+# -*- coding: utf-8 -*-
+"""
+Unit tests for Store Factory functionality
+"""
+
+import pytest
+from unittest.mock import patch, MagicMock
+
+from store.xhs import XhsStoreFactory
+from store.xhs._store_impl import (
+    XhsCsvStoreImplement,
+    XhsJsonStoreImplement,
+    XhsDbStoreImplement,
+    XhsSqliteStoreImplement,
+    XhsMongoStoreImplement,
+    XhsExcelStoreImplement
+)
+
+
+class TestXhsStoreFactory:
+    """Test cases for XhsStoreFactory"""
+    
+    @patch('config.SAVE_DATA_OPTION', 'csv')
+    def test_create_csv_store(self):
+        """Test creating CSV store"""
+        store = XhsStoreFactory.create_store()
+        assert isinstance(store, XhsCsvStoreImplement)
+    
+    @patch('config.SAVE_DATA_OPTION', 'json')
+    def test_create_json_store(self):
+        """Test creating JSON store"""
+        store = XhsStoreFactory.create_store()
+        assert isinstance(store, XhsJsonStoreImplement)
+    
+    @patch('config.SAVE_DATA_OPTION', 'db')
+    def test_create_db_store(self):
+        """Test creating database store"""
+        store = XhsStoreFactory.create_store()
+        assert isinstance(store, XhsDbStoreImplement)
+    
+    @patch('config.SAVE_DATA_OPTION', 'sqlite')
+    def test_create_sqlite_store(self):
+        """Test creating SQLite store"""
+        store = XhsStoreFactory.create_store()
+        assert isinstance(store, XhsSqliteStoreImplement)
+    
+    @patch('config.SAVE_DATA_OPTION', 'mongodb')
+    def test_create_mongodb_store(self):
+        """Test creating MongoDB store"""
+        store = XhsStoreFactory.create_store()
+        assert isinstance(store, XhsMongoStoreImplement)
+    
+    @patch('config.SAVE_DATA_OPTION', 'excel')
+    @patch('var.crawler_type_var.get', return_value='search')
+    def test_create_excel_store(self, mock_crawler_type):
+        """Test creating Excel store"""
+        store = XhsStoreFactory.create_store()
+        assert isinstance(store, XhsExcelStoreImplement)
+    
+    @patch('config.SAVE_DATA_OPTION', 'invalid')
+    def test_invalid_store_option(self):
+        """Test that invalid store option raises ValueError"""
+        with pytest.raises(ValueError) as exc_info:
+            XhsStoreFactory.create_store()
+        
+        assert "Invalid save option" in str(exc_info.value)
+    
+    def test_all_stores_registered(self):
+        """Test that all store types are registered"""
+        expected_stores = ['csv', 'json', 'db', 'sqlite', 'mongodb', 'excel']
+        
+        for store_type in expected_stores:
+            assert store_type in XhsStoreFactory.STORES
+        
+        assert len(XhsStoreFactory.STORES) == len(expected_stores)