Add endpoint to return the summary data for returned letters.

Returning the count of letters that are returned for each report date.

tests/app/db.py

@@ -950,11 +950,11 @@ def create_returned_letter(service, reported_at=None):
     template = create_template(service=service, template_type=LETTER_TYPE)
     notification = create_notification(template=template, status=NOTIFICATION_RETURNED_LETTER)
     returned_letter = ReturnedLetter(
-        service_id= service.id,
-        reported_at= reported_at or datetime.utcnow(),
-        notification_id= notification.id
+        service_id=service.id,
+        reported_at=reported_at or datetime.utcnow(),
+        notification_id=notification.id
     )
 
     db.session.add(returned_letter)
     db.session.commit()
-    return returned_letter
+    return returned_letter

tests/app/service/test_rest.py

@@ -47,7 +47,7 @@ from tests.app.db import (
     create_domain,
     create_email_branding,
     create_annual_billing,
-)
+    create_returned_letter)
 from tests.app.db import create_user
 
 
@@ -3372,3 +3372,12 @@ def test_get_monthly_notification_data_by_service(mocker, admin_request):
 
     dao_mock.assert_called_once_with(start_date, end_date)
     assert response == []
+
+
+def test_get_returned_letter_summary(admin_request, sample_service):
+    create_returned_letter(sample_service, reported_at=datetime.utcnow())
+    create_returned_letter(sample_service, reported_at=datetime.utcnow()-timedelta(days=3))
+
+    response = admin_request.get('service.returned_letter_summary', service_id=sample_service.id)
+
+    assert len(response) == 2