Add "charged_units" to service usage APIs

This can be calculated from the "free_allowance_used" field and the
"chargeable_units" field, but having it included separately is more
convenient as it can be used directly in Admin [^1].

[^1]: 417e7370bb/app/templates/views/usage.html (L38-L39)

tests/app/billing/test_rest.py

@@ -178,6 +178,7 @@ def test_get_yearly_usage_by_monthly_from_ft_billing(admin_request, notify_db_se
     assert letter_row["postage"] == "second"
     assert letter_row["cost"] == 9.9
     assert letter_row["free_allowance_used"] == 0
+    assert letter_row["charged_units"] == 30
 
     assert sms_row["month"] == "April"
     assert sms_row["notification_type"] == "sms"
@@ -189,6 +190,7 @@ def test_get_yearly_usage_by_monthly_from_ft_billing(admin_request, notify_db_se
     # free allowance is 4, so (30 - 4) * 0.162
     assert sms_row["cost"] == 4.212
     assert sms_row["free_allowance_used"] == 4
+    assert sms_row["charged_units"] == 26
 
 
 def set_up_yearly_data():
@@ -263,6 +265,7 @@ def test_get_yearly_billing_usage_summary_from_ft_billing(admin_request, notify_
     assert json_response[0]['letter_total'] == 0
     assert json_response[0]['cost'] == 0
     assert json_response[0]['free_allowance_used'] == 0
+    assert json_response[0]['charged_units'] == 0
 
     assert json_response[1]['notification_type'] == 'letter'
     assert json_response[1]['billing_units'] == 275
@@ -272,6 +275,7 @@ def test_get_yearly_billing_usage_summary_from_ft_billing(admin_request, notify_
     assert json_response[1]['letter_total'] == 90.75
     assert json_response[1]['cost'] == 90.75
     assert json_response[1]['free_allowance_used'] == 0
+    assert json_response[1]['charged_units'] == 275
 
     assert json_response[2]['notification_type'] == 'sms'
     assert json_response[2]['billing_units'] == 825
@@ -281,3 +285,4 @@ def test_get_yearly_billing_usage_summary_from_ft_billing(admin_request, notify_
     assert json_response[2]['letter_total'] == 0
     assert json_response[2]['cost'] == 13.3002
     assert json_response[2]['free_allowance_used'] == 4
+    assert json_response[2]['charged_units'] == 821

tests/app/dao/test_ft_billing_dao.py

@@ -439,6 +439,7 @@ def test_fetch_monthly_billing_for_year(notify_db_session):
     assert results[0].rate == Decimal('0')
     assert results[0].cost == Decimal('0')
     assert results[0].free_allowance_used == 0
+    assert results[0].charged_units == 0
 
     assert str(results[1].month) == "2016-04-01"
     assert results[1].notification_type == 'letter'
@@ -448,6 +449,7 @@ def test_fetch_monthly_billing_for_year(notify_db_session):
     assert results[1].rate == Decimal('0.30')
     assert results[1].cost == Decimal('9')
     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'
@@ -457,6 +459,7 @@ def test_fetch_monthly_billing_for_year(notify_db_session):
     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'
@@ -467,6 +470,7 @@ def test_fetch_monthly_billing_for_year(notify_db_session):
     # 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 str(results[4].month) == "2016-05-01"
     assert str(results[47].month) == "2017-03-01"
@@ -488,6 +492,7 @@ def test_fetch_monthly_billing_for_year_variable_rates(notify_db_session):
     assert results[0].rate == Decimal('0.33')
     assert results[0].cost == Decimal('0.33')
     assert results[0].free_allowance_used == 0
+    assert results[0].charged_units == 1
 
     assert str(results[1].month) == "2018-05-01"
     assert results[1].notification_type == 'letter'
@@ -497,6 +502,7 @@ def test_fetch_monthly_billing_for_year_variable_rates(notify_db_session):
     assert results[1].rate == Decimal('0.36')
     assert results[1].cost == Decimal('0.72')
     assert results[1].free_allowance_used == 0
+    assert results[1].charged_units == 2
 
     assert str(results[2].month) == "2018-05-01"
     assert results[2].notification_type == 'sms'
@@ -507,6 +513,7 @@ def test_fetch_monthly_billing_for_year_variable_rates(notify_db_session):
     # 1 free units on the 17th
     assert results[2].cost == Decimal('0.045')
     assert results[2].free_allowance_used == 1
+    assert results[2].charged_units == 3
 
     assert str(results[3].month) == "2018-05-01"
     assert results[3].notification_type == 'sms'
@@ -517,6 +524,7 @@ def test_fetch_monthly_billing_for_year_variable_rates(notify_db_session):
     # 5 free units on the 16th
     assert results[3].cost == Decimal('0')
     assert results[3].free_allowance_used == 5
+    assert results[3].charged_units == 0
 
 
 @freeze_time('2018-08-01 13:30:00')
@@ -552,6 +560,7 @@ def test_fetch_billing_totals_for_year(notify_db_session):
     assert results[0].rate == Decimal('0')
     assert results[0].cost == Decimal('0')
     assert results[0].free_allowance_used == 0
+    assert results[0].charged_units == 0
 
     assert results[1].notification_type == 'letter'
     assert results[1].notifications_sent == 365
@@ -560,6 +569,7 @@ def test_fetch_billing_totals_for_year(notify_db_session):
     assert results[1].rate == Decimal('0.3')
     assert results[1].cost == Decimal('109.5')
     assert results[1].free_allowance_used == 0
+    assert results[1].charged_units == 365
 
     assert results[2].notification_type == 'letter'
     assert results[2].notifications_sent == 365
@@ -568,6 +578,7 @@ def test_fetch_billing_totals_for_year(notify_db_session):
     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
@@ -576,6 +587,7 @@ def test_fetch_billing_totals_for_year(notify_db_session):
     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
 
 
 def test_fetch_billing_totals_for_year_uses_current_annual_billing(notify_db_session):
@@ -606,6 +618,7 @@ def test_fetch_billing_totals_for_year_variable_rates(notify_db_session):
     assert results[0].rate == Decimal('0.33')
     assert results[0].cost == Decimal('0.33')
     assert results[0].free_allowance_used == 0
+    assert results[0].charged_units == 1
 
     assert results[1].notification_type == 'letter'
     assert results[1].notifications_sent == 2
@@ -614,6 +627,7 @@ def test_fetch_billing_totals_for_year_variable_rates(notify_db_session):
     assert results[1].rate == Decimal('0.36')
     assert results[1].cost == Decimal('0.72')
     assert results[1].free_allowance_used == 0
+    assert results[1].charged_units == 2
 
     assert results[2].notification_type == 'sms'
     assert results[2].notifications_sent == 1
@@ -623,6 +637,7 @@ def test_fetch_billing_totals_for_year_variable_rates(notify_db_session):
     # 1 free unit on the 17th
     assert results[2].cost == Decimal('0.045')
     assert results[2].free_allowance_used == 1
+    assert results[2].charged_units == 3
 
     assert results[3].notification_type == 'sms'
     assert results[3].notifications_sent == 2
@@ -632,6 +647,7 @@ def test_fetch_billing_totals_for_year_variable_rates(notify_db_session):
     # 5 free units on the 16th
     assert results[3].cost == Decimal('0')
     assert results[3].free_allowance_used == 5
+    assert results[3].charged_units == 0
 
 
 def test_delete_billing_data(notify_db_session):