Refactor code

- Created TaskNames for DVLA_FILES rather than have DVLA_FILES in QueueNames
- Removed PROCESS_FTP from all_queues() as this was causing problems in picking up letter job tasks
- Created test to ensure that we don't arbitrarily add queue names to all_queues

app/letters/rest.py

@@ -2,7 +2,7 @@ from flask import Blueprint, jsonify
 from flask import request
 
 from app import notify_celery
-from app.config import QueueNames
+from app.config import QueueNames, TaskNames
 from app.dao.jobs_dao import dao_get_all_letter_jobs
 from app.schemas import job_schema
 from app.v2.errors import register_errors
@@ -16,7 +16,7 @@ register_errors(letter_job)
 @letter_job.route('/send-letter-jobs', methods=['POST'])
 def send_letter_jobs():
     job_ids = validate(request.get_json(), letter_job_ids)
-    notify_celery.send_task(name=QueueNames.DVLA_FILES, args=(job_ids['job_ids'],), queue=QueueNames.PROCESS_FTP)
+    notify_celery.send_task(name=TaskNames.DVLA_FILES, args=(job_ids['job_ids'],), queue=QueueNames.PROCESS_FTP)
 
     return jsonify(data={"response": "Task created to send files to DVLA"}), 201