SMS service test file error catching and import editing

- ApiException import path fixed
- Unnecessary import line removed
- Error catching scenario in test file improved

Author: onder-aycicek

tests/test_sms_service.py

@@ -7,7 +7,7 @@
 import os
 from dotenv import load_dotenv
 from netgsm import Netgsm
-from netgsm.exceptions import ApiException
+from netgsm.exceptions.api_exception import ApiException
 
 
 class TestSmsService(unittest.TestCase):
@@ -68,7 +68,6 @@ def test_send_sms_failure(self, mock_post):
         Tests SMS sending failure case.
         """
         # Set up to throw ApiException
-        from netgsm.exceptions.api_exception import ApiException
         mock_post.side_effect = ApiException("API error")
 
         # Specify that we expect an error