Remove redundant test data for usage DAOs

This is unnecessary since we now have separate "_variable_rates"
tests that check the behaviour for multiple rates explicitly for
the two types of notifications it affects.

tests/app/dao/test_ft_billing_dao.py

@@ -50,7 +50,6 @@ def set_up_yearly_data():
     for dt in (date(2016, 3, 31), date(2017, 4, 1)):
         create_ft_billing(bst_date=dt, template=sms_template, rate=0.163)
         create_ft_billing(bst_date=dt, template=email_template, rate=0, billable_unit=0)
-        create_ft_billing(bst_date=dt, template=letter_template, rate=0.34, postage='second')
         create_ft_billing(bst_date=dt, template=letter_template, rate=0.31, postage='second')
 
     start_date = date(2016, 4, 1)
@@ -61,7 +60,6 @@ def set_up_yearly_data():
 
         create_ft_billing(bst_date=dt, template=sms_template, rate=0.162)
         create_ft_billing(bst_date=dt, template=email_template, rate=0, billable_unit=0)
-        create_ft_billing(bst_date=dt, template=letter_template, rate=0.33, postage='second')
         create_ft_billing(bst_date=dt, template=letter_template, rate=0.30, postage='second')
 
     return service
@@ -429,7 +427,7 @@ def test_fetch_monthly_billing_for_year(notify_db_session):
     create_annual_billing(service_id=service.id, free_sms_fragment_limit=10, financial_year_start=2016)
     results = fetch_monthly_billing_for_year(service.id, 2016)
 
-    assert len(results) == 48
+    assert len(results) == 36
 
     assert str(results[0].month) == "2016-04-01"
     assert results[0].notification_type == 'email'
@@ -451,29 +449,19 @@ def test_fetch_monthly_billing_for_year(notify_db_session):
     assert results[1].free_allowance_used == 0
     assert results[1].charged_units == 30
 
-    assert str(results[1].month) == "2016-04-01"
-    assert results[2].notification_type == 'letter'
+    assert str(results[2].month) == "2016-04-01"
+    assert results[2].notification_type == 'sms'
     assert results[2].notifications_sent == 30
     assert results[2].billable_units == 30
     assert results[2].chargeable_units == 30
-    assert results[2].rate == Decimal('0.33')
-    assert results[2].cost == Decimal('9.9')
-    assert results[2].free_allowance_used == 0
-    assert results[2].charged_units == 30
-
-    assert str(results[3].month) == "2016-04-01"
-    assert results[3].notification_type == 'sms'
-    assert results[3].notifications_sent == 30
-    assert results[3].billable_units == 30
-    assert results[3].chargeable_units == 30
-    assert results[3].rate == Decimal('0.162')
+    assert results[2].rate == Decimal('0.162')
     # free allowance is 10, so (30 - 10) * 0.162
-    assert results[3].cost == Decimal('3.24')
-    assert results[3].free_allowance_used == 10
-    assert results[3].charged_units == 20
+    assert results[2].cost == Decimal('3.24')
+    assert results[2].free_allowance_used == 10
+    assert results[2].charged_units == 20
 
-    assert str(results[4].month) == "2016-05-01"
-    assert str(results[47].month) == "2017-03-01"
+    assert str(results[3].month) == "2016-05-01"
+    assert str(results[35].month) == "2017-03-01"
 
 
 def test_fetch_monthly_billing_for_year_variable_rates(notify_db_session):
@@ -552,7 +540,7 @@ def test_fetch_billing_totals_for_year(notify_db_session):
     create_annual_billing(service_id=service.id, free_sms_fragment_limit=1000, financial_year_start=2016)
     results = fetch_billing_totals_for_year(service_id=service.id, year=2016)
 
-    assert len(results) == 4
+    assert len(results) == 3
     assert results[0].notification_type == 'email'
     assert results[0].notifications_sent == 365
     assert results[0].billable_units == 365
@@ -571,23 +559,14 @@ def test_fetch_billing_totals_for_year(notify_db_session):
     assert results[1].free_allowance_used == 0
     assert results[1].charged_units == 365
 
-    assert results[2].notification_type == 'letter'
+    assert results[2].notification_type == 'sms'
     assert results[2].notifications_sent == 365
     assert results[2].billable_units == 365
     assert results[2].chargeable_units == 365
-    assert results[2].rate == Decimal('0.33')
-    assert results[2].cost == Decimal('120.45')
-    assert results[2].free_allowance_used == 0
-    assert results[2].charged_units == 365
-
-    assert results[3].notification_type == 'sms'
-    assert results[3].notifications_sent == 365
-    assert results[3].billable_units == 365
-    assert results[3].chargeable_units == 365
-    assert results[3].rate == Decimal('0.162')
-    assert results[3].cost == Decimal('0')
-    assert results[3].free_allowance_used == 365
-    assert results[3].charged_units == 0
+    assert results[2].rate == Decimal('0.162')
+    assert results[2].cost == Decimal('0')
+    assert results[2].free_allowance_used == 365
+    assert results[2].charged_units == 0
 
 
 def test_fetch_billing_totals_for_year_uses_current_annual_billing(notify_db_session):