Update letter notification processing for letter pdfs in research mode

- calls create fake response file to allow functional tests to run and trigger update of status to delivered only on preview and development so that FT response files don't pollute staging and live buckets

app/v2/notifications/post_notifications.py

@@ -6,6 +6,7 @@ from notifications_utils.recipients import try_validate_and_format_phone_number
 
 from app import api_user, authenticated_service
 from app.config import QueueNames
+from app.dao.notifications_dao import update_notification_status_by_reference
 from app.models import (
     SMS_TYPE,
     EMAIL_TYPE,
@@ -14,9 +15,11 @@ from app.models import (
     KEY_TYPE_TEST,
     KEY_TYPE_TEAM,
     NOTIFICATION_CREATED,
-    NOTIFICATION_SENDING
+    NOTIFICATION_SENDING,
+    NOTIFICATION_DELIVERED
 )
 from app.celery.letters_pdf_tasks import create_letters_pdf
+from app.celery.research_mode_tasks import create_fake_letter_response_file
 from app.celery.tasks import update_letter_notifications_to_sent_to_dvla
 from app.notifications.process_notifications import (
     persist_notification,
@@ -171,7 +174,7 @@ def process_letter_notification(*, letter_data, api_key, template, reply_to_text
     if api_key.key_type == KEY_TYPE_TEAM:
         raise BadRequestError(message='Cannot send letters with a team api key', status_code=403)
 
-    if api_key.service.restricted and api_key.key_type != KEY_TYPE_TEST:
+    if not api_key.service.research_mode and api_key.service.restricted and api_key.key_type != KEY_TYPE_TEST:
         raise BadRequestError(message='Cannot send letters when service is in trial mode', status_code=403)
 
     should_send = not (api_key.service.research_mode or api_key.key_type == KEY_TYPE_TEST)
@@ -191,10 +194,19 @@ def process_letter_notification(*, letter_data, api_key, template, reply_to_text
         )
 
     if api_key.service.has_permission('letters_as_pdf'):
-        create_letters_pdf.apply_async(
-            [str(notification.id)],
-            queue=QueueNames.CREATE_LETTERS_PDF
-        )
+        if should_send:
+            create_letters_pdf.apply_async(
+                [str(notification.id)],
+                queue=QueueNames.CREATE_LETTERS_PDF
+            )
+        elif (api_key.service.research_mode and
+              current_app.config['NOTIFY_ENVIRONMENT'] in ['preview', 'development']):
+            create_fake_letter_response_file.apply_async(
+                (notification.reference,),
+                queue=QueueNames.RESEARCH_MODE
+            )
+        else:
+            update_notification_status_by_reference(notification.reference, NOTIFICATION_DELIVERED)
 
     return notification