Add postage for send-one-off letters.

The postage is set to europe or rest-of-world for international letters, otherwise the template postage is used.

Also set international for letters.

tests/app/notifications/test_validators.py

@@ -5,7 +5,12 @@ from notifications_utils import SMS_CHAR_COUNT_LIMIT
 
 import app
 from app.dao import templates_dao
-from app.models import SMS_TYPE, EMAIL_TYPE, LETTER_TYPE
+from app.models import (
+    EMAIL_TYPE,
+    INTERNATIONAL_LETTERS,
+    LETTER_TYPE,
+    SMS_TYPE,
+)
 from app.notifications.process_notifications import create_content_for_notification
 from app.notifications.validators import (
     check_content_char_count,
@@ -20,6 +25,7 @@ from app.notifications.validators import (
     check_service_letter_contact_id,
     check_reply_to,
     service_can_send_to_recipient,
+    validate_address,
     validate_and_format_recipient,
     validate_template,
 )
@@ -619,3 +625,19 @@ def test_check_if_service_can_send_files_by_email_passes_if_contact_link_set(sam
         service_contact_link=sample_service.contact_link,
         service_id=sample_service.id
     )
+
+
+@pytest.mark.parametrize('key, address_line_3, expected_postage',
+                         [('address_line_3', 'SW1 1AA', None),
+                          ('address_line_5', 'CANADA', 'rest-of-world'),
+                          ('address_line_3', 'GERMANY', 'europe')
+                          ])
+def test_validate_address(notify_db_session, key, address_line_3, expected_postage):
+    service = create_service(service_permissions=[LETTER_TYPE, INTERNATIONAL_LETTERS])
+    data = {
+        'address_line_1': 'Prince Harry',
+        'address_line_2': 'Toronto',
+        key: address_line_3,
+    }
+    postage = validate_address(service, data)
+    assert postage == expected_postage