only send letters in created state to ftp app for zipping

this means if we end up with some notifications sending and others not,
due to problems with the ftp connectivity for example, we don't re-send
those that worked.

As a reminder, letter pdf notifications start as created and stay that
way until we have sent the zip file to DVLA, at which point they are
updated to sending
 #

tests/app/celery/test_letters_pdf_tasks.py

@@ -11,9 +11,10 @@ from app.celery.letters_pdf_tasks import (
     create_letters_pdf,
     get_letters_pdf,
     collate_letter_pdfs_for_day,
-    group_letters
+    group_letters,
+    letter_in_created_state,
 )
-from app.models import Notification
+from app.models import Notification, NOTIFICATION_SENDING
 
 from tests.conftest import set_config_values
 
@@ -166,7 +167,8 @@ def test_collate_letter_pdfs_for_day(notify_api, mocker):
     )
 
 
-def test_group_letters_splits_on_file_size(notify_api):
+def test_group_letters_splits_on_file_size(notify_api, mocker):
+    mocker.patch('app.celery.letters_pdf_tasks.letter_in_created_state', return_value=True)
     letters = [
         # ends under max but next one is too big
         {'Key': 'A.pdf', 'Size': 1}, {'Key': 'B.pdf', 'Size': 2},
@@ -192,7 +194,8 @@ def test_group_letters_splits_on_file_size(notify_api):
         assert next(x, None) is None
 
 
-def test_group_letters_splits_on_file_count(notify_api):
+def test_group_letters_splits_on_file_count(notify_api, mocker):
+    mocker.patch('app.celery.letters_pdf_tasks.letter_in_created_state', return_value=True)
     letters = [
         {'Key': 'A.pdf', 'Size': 1},
         {'Key': 'B.pdf', 'Size': 2},
@@ -215,7 +218,8 @@ def test_group_letters_splits_on_file_count(notify_api):
         assert next(x, None) is None
 
 
-def test_group_letters_splits_on_file_size_and_file_count(notify_api):
+def test_group_letters_splits_on_file_size_and_file_count(notify_api, mocker):
+    mocker.patch('app.celery.letters_pdf_tasks.letter_in_created_state', return_value=True)
     letters = [
         # ends under max file size but next file is too big
         {'Key': 'A.pdf', 'Size': 1},
@@ -249,10 +253,39 @@ def test_group_letters_splits_on_file_size_and_file_count(notify_api):
         assert next(x, None) is None
 
 
-def test_group_letters_ignores_non_pdfs(notify_api):
+def test_group_letters_ignores_non_pdfs(notify_api, mocker):
+    mocker.patch('app.celery.letters_pdf_tasks.letter_in_created_state', return_value=True)
     letters = [{'Key': 'A.zip'}]
     assert list(group_letters(letters)) == []
 
 
-def test_group_letters_with_no_letters(notify_api):
+def test_group_letters_ignores_notifications_already_sent(notify_api, mocker):
+    mock = mocker.patch('app.celery.letters_pdf_tasks.letter_in_created_state', return_value=False)
+    letters = [{'Key': 'A.pdf'}]
+    assert list(group_letters(letters)) == []
+    mock.assert_called_once_with('A.pdf')
+
+
+def test_group_letters_with_no_letters(notify_api, mocker):
+    mocker.patch('app.celery.letters_pdf_tasks.letter_in_created_state', return_value=True)
     assert list(group_letters([])) == []
+
+
+def test_letter_in_created_state(sample_notification):
+    sample_notification.reference = 'ABCDEF1234567890'
+    filename = '2018-01-13/NOTIFY.ABCDEF1234567890.D.2.C.C.20180113120000.PDF'
+
+    assert letter_in_created_state(filename) is True
+
+
+def test_letter_in_created_state_fails_if_notification_not_in_created(sample_notification):
+    sample_notification.reference = 'ABCDEF1234567890'
+    sample_notification.status = NOTIFICATION_SENDING
+    filename = '2018-01-13/NOTIFY.ABCDEF1234567890.D.2.C.C.20180113120000.PDF'
+    assert letter_in_created_state(filename) is False
+
+
+def test_letter_in_created_state_fails_if_notification_doesnt_exist(sample_notification):
+    sample_notification.reference = 'QWERTY1234567890'
+    filename = '2018-01-13/NOTIFY.ABCDEF1234567890.D.2.C.C.20180113120000.PDF'
+    assert letter_in_created_state(filename) is False