fix: add null safety check to URL construction in test_login.py

- Add explicit check for ERP_URL environment variable
- Prevent AttributeError when ERP_URL is not set
- Provide clear error message for missing configuration

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_login.py

@@ -32,7 +32,10 @@ print(f"  Headless: {os.getenv('ERP_HEADLESS')}")
 print(f"  Ignore HTTPS Errors: {os.getenv('ERP_IGNORE_HTTPS_ERRORS')}")
 
 # Construct complete login URL
-url = f"{os.getenv('ERP_URL').rstrip('/')}/yonbip/resources/uap/rbac/login/main/index.html"
+base_url = os.getenv('ERP_URL')
+if not base_url:
+    raise ValueError("ERP_URL environment variable is required")
+url = f"{base_url.rstrip('/')}/yonbip/resources/uap/rbac/login/main/index.html"
 
 try:
     with sync_playwright() as p: