Write some pseudo code for ft billing

tests/app/dao/test_ft_billing_dao.py

@@ -1,8 +1,11 @@
 from datetime import datetime
 from decimal import Decimal
 
-from app.dao.fact_billing_dao import fetch_annual_billing_by_month
-from tests.app.db import create_ft_billing, create_service, create_template
+from freezegun import freeze_time
+
+from app.dao.date_util import get_month_start_and_end_date_in_utc
+from app.dao.fact_billing_dao import fetch_annual_billing_by_month, need_deltas
+from tests.app.db import create_ft_billing, create_service, create_template, create_notification
 
 
 def test_fetch_annual_billing_by_month(notify_db_session):
@@ -22,3 +25,18 @@ def test_fetch_annual_billing_by_month(notify_db_session):
     assert results[0] == (31, Decimal('31'), service.id, 'email', Decimal('0'), Decimal('1'), False)
     assert month == datetime(2018, 1, 1)
 
+
+@freeze_time("2018-01-21 13:00:00")
+def test_need_deltas(notify_db_session):
+    service = create_service()
+    template = create_template(service=service, template_type="email")
+    for i in range(1, 21):
+        record = create_ft_billing(bst_date='2018-01-{}'.format(i),
+                                   service=service,
+                                   template=template,
+                                   notification_type='email')
+    start_date, end_date = get_month_start_and_end_date_in_utc(datetime.utcnow())
+
+    result = need_deltas(start_date=start_date, end_date=end_date,
+                         service_id=service.id, notification_type='email')
+    assert result