Fix incorrect chargeable_units column

This was added to migrate away from the vague "billing_units" field,
but without fixing the inconsistent data behind it:

- For emails and letters, "billing_units" was just the number sent.

- For SMS, "billing_units" really was the chargeable_units.

To avoid confusion we need two fields to represent the original mix
of data - this exposes "notifications_sent" in both APIs.

app/billing/billing_schemas.py

@@ -17,9 +17,15 @@ def serialize_ft_billing_remove_emails(rows):
         {
             "month": (datetime.strftime(row.month, "%B")),
             "notification_type": row.notification_type,
+            # TEMPORARY: while we migrate to "chargeable_units" in the Admin app
             "billing_units": row.billable_units,
+            "chargeable_units": row.chargeable_units,
             "rate": float(row.rate),
             "postage": row.postage,
+            "cost": float(row.cost),
+            "free_chargeable_units": row.free_chargeable_units,
+            "charged_units": row.charged_units,
+            "notifications_sent": row.notifications_sent,
         }
         for row in rows
         if row.notification_type != 'email'
@@ -30,9 +36,16 @@ def serialize_ft_billing_yearly_totals(rows):
     return [
         {
             "notification_type": row.notification_type,
+            # TEMPORARY: while we migrate to "chargeable_units" in the Admin app
             "billing_units": row.billable_units,
+            "chargeable_units": row.chargeable_units,
             "rate": float(row.rate),
+            # TEMPORARY: while we migrate to "cost" in the Admin app
             "letter_total": float(row.billable_units * row.rate) if row.notification_type == 'letter' else 0,
+            "cost": float(row.cost),
+            "free_chargeable_units": row.free_chargeable_units,
+            "charged_units": row.charged_units,
+            "notifications_sent": row.notifications_sent,
         }
         for row in rows
     ]

app/dao/fact_billing_dao.py

@@ -2,7 +2,7 @@ from datetime import date, datetime, timedelta
 
 from flask import current_app
 from notifications_utils.timezones import convert_utc_to_bst
-from sqlalchemy import Date, Integer, and_, desc, func
+from sqlalchemy import Date, Integer, and_, desc, func, union
 from sqlalchemy.dialects.postgresql import insert
 from sqlalchemy.sql.expression import case, literal
 
@@ -197,55 +197,36 @@ def fetch_letter_line_items_for_all_services(start_date, end_date):
 
 
 def fetch_billing_totals_for_year(service_id, year):
-    year_start, year_end = get_financial_year_dates(year)
-    """
-      Billing for email: only record the total number of emails.
-      Billing for letters: The billing units is used to fetch the correct rate for the sheet count of the letter.
-      Total cost is notifications_sent * rate.
-      Rate multiplier does not apply to email or letters.
-    """
-    email_and_letters = db.session.query(
-        func.sum(FactBilling.notifications_sent).label("notifications_sent"),
-        func.sum(FactBilling.notifications_sent).label("billable_units"),
-        FactBilling.rate.label('rate'),
-        FactBilling.notification_type.label('notification_type')
-    ).filter(
-        FactBilling.service_id == service_id,
-        FactBilling.bst_date >= year_start,
-        FactBilling.bst_date <= year_end,
-        FactBilling.notification_type.in_([EMAIL_TYPE, LETTER_TYPE])
-    ).group_by(
-        FactBilling.rate,
-        FactBilling.notification_type
-    )
-    """
-    Billing for SMS using the billing_units * rate_multiplier. Billing unit of SMS is the fragment count of a message
-    """
-    sms = db.session.query(
-        func.sum(FactBilling.notifications_sent).label("notifications_sent"),
-        func.sum(FactBilling.billable_units * FactBilling.rate_multiplier).label("billable_units"),
-        FactBilling.rate,
-        FactBilling.notification_type
-    ).filter(
-        FactBilling.service_id == service_id,
-        FactBilling.bst_date >= year_start,
-        FactBilling.bst_date <= year_end,
-        FactBilling.notification_type == SMS_TYPE
-    ).group_by(
-        FactBilling.rate,
-        FactBilling.notification_type
-    )
-
-    yearly_data = email_and_letters.union_all(sms).order_by(
-        'notification_type',
-        'rate'
+    return db.session.query(
+        union(*[
+            db.session.query(
+                func.sum(query.c.notifications_sent).label("notifications_sent"),
+                # TEMPORARY: while we switch to "chargeable units"
+                func.sum(query.c.billable_units).label("billable_units"),
+                func.sum(query.c.chargeable_units).label("chargeable_units"),
+                query.c.rate.label("rate"),
+                query.c.notification_type.label("notification_type"),
+                func.sum(query.c.cost).label("cost"),
+                func.sum(query.c.free_chargeable_units).label("free_chargeable_units"),
+                func.sum(query.c.charged_units).label("charged_units"),
+            ).group_by(
+                query.c.rate,
+                query.c.notification_type
+            )
+            for query in [
+                query_service_sms_usage_for_year(service_id, year).subquery(),
+                query_service_email_usage_for_year(service_id, year).subquery(),
+                query_service_letter_usage_for_year(service_id, year).subquery(),
+            ]
+        ]).subquery()
+    ).order_by(
+        "notification_type",
+        "rate",
     ).all()
 
-    return yearly_data
-
 
 def fetch_monthly_billing_for_year(service_id, year):
-    year_start, year_end = get_financial_year_dates(year)
+    _, year_end = get_financial_year_dates(year)
     today = convert_utc_to_bst(datetime.utcnow()).date()
 
     # if year end date is less than today, we are calculating for data in the past and have no need for deltas.
@@ -254,51 +235,141 @@ def fetch_monthly_billing_for_year(service_id, year):
         for d in data:
             update_fact_billing(data=d, process_day=today)
 
-    email_and_letters = db.session.query(
-        func.date_trunc('month', FactBilling.bst_date).cast(Date).label("month"),
-        func.sum(FactBilling.notifications_sent).label("notifications_sent"),
-        func.sum(FactBilling.notifications_sent).label("billable_units"),
-        FactBilling.rate.label('rate'),
-        FactBilling.notification_type.label('notification_type'),
-        FactBilling.postage
-    ).filter(
-        FactBilling.service_id == service_id,
-        FactBilling.bst_date >= year_start,
-        FactBilling.bst_date <= year_end,
-        FactBilling.notification_type.in_([EMAIL_TYPE, LETTER_TYPE])
-    ).group_by(
-        'month',
-        FactBilling.rate,
-        FactBilling.notification_type,
-        FactBilling.postage
-    )
-
-    sms = db.session.query(
-        func.date_trunc('month', FactBilling.bst_date).cast(Date).label("month"),
-        func.sum(FactBilling.notifications_sent).label("notifications_sent"),
-        func.sum(FactBilling.billable_units * FactBilling.rate_multiplier).label("billable_units"),
-        FactBilling.rate,
-        FactBilling.notification_type,
-        FactBilling.postage
-    ).filter(
-        FactBilling.service_id == service_id,
-        FactBilling.bst_date >= year_start,
-        FactBilling.bst_date <= year_end,
-        FactBilling.notification_type == SMS_TYPE
-    ).group_by(
-        'month',
-        FactBilling.rate,
-        FactBilling.notification_type,
-        FactBilling.postage
-    )
-
-    yearly_data = email_and_letters.union_all(sms).order_by(
-        'month',
-        'notification_type',
-        'rate'
+    return db.session.query(
+        union(*[
+            db.session.query(
+                func.date_trunc('month', query.c.bst_date).cast(Date).label("month"),
+                func.sum(query.c.notifications_sent).label("notifications_sent"),
+                # TEMPORARY: while we switch to "chargeable units"
+                func.sum(query.c.billable_units).label("billable_units"),
+                func.sum(query.c.chargeable_units).label("chargeable_units"),
+                query.c.rate.label("rate"),
+                query.c.postage.label("postage"),
+                query.c.notification_type.label("notification_type"),
+                func.sum(query.c.cost).label("cost"),
+                func.sum(query.c.free_chargeable_units).label("free_chargeable_units"),
+                func.sum(query.c.charged_units).label("charged_units"),
+            ).group_by(
+                query.c.rate,
+                query.c.notification_type,
+                query.c.postage,
+                'month',
+            )
+            for query in [
+                query_service_sms_usage_for_year(service_id, year).subquery(),
+                query_service_email_usage_for_year(service_id, year).subquery(),
+                query_service_letter_usage_for_year(service_id, year).subquery(),
+            ]
+        ]).subquery()
+    ).order_by(
+        "month",
+        "notification_type",
+        "rate",
     ).all()
 
-    return yearly_data
+
+def query_service_email_usage_for_year(service_id, year):
+    year_start, year_end = get_financial_year_dates(year)
+
+    return db.session.query(
+        FactBilling.bst_date,
+        FactBilling.postage,  # should always be "none"
+        FactBilling.notifications_sent,
+        # TEMPORARY: while we switch to "chargeable units"
+        FactBilling.notifications_sent.label("billable_units"),
+        FactBilling.billable_units.label("chargeable_units"),
+        FactBilling.rate,
+        FactBilling.notification_type,
+        FactBilling.notifications_sent.label("charged_units"),
+        literal(0).label("free_chargeable_units"),
+        literal(0).label("cost"),
+    ).filter(
+        FactBilling.service_id == service_id,
+        FactBilling.bst_date >= year_start,
+        FactBilling.bst_date <= year_end,
+        FactBilling.notification_type == EMAIL_TYPE
+    )
+
+
+def query_service_letter_usage_for_year(service_id, year):
+    year_start, year_end = get_financial_year_dates(year)
+
+    return db.session.query(
+        FactBilling.bst_date,
+        FactBilling.postage,
+        FactBilling.notifications_sent,
+        # TEMPORARY: while we switch to "chargeable units"
+        FactBilling.notifications_sent.label("billable_units"),
+        FactBilling.billable_units.label("chargeable_units"),
+        FactBilling.rate,
+        FactBilling.notification_type,
+        FactBilling.notifications_sent.label("charged_units"),
+        literal(0).label("free_chargeable_units"),
+        (FactBilling.notifications_sent * FactBilling.rate).label("cost"),
+    ).filter(
+        FactBilling.service_id == service_id,
+        FactBilling.bst_date >= year_start,
+        FactBilling.bst_date <= year_end,
+        FactBilling.notification_type == LETTER_TYPE
+    )
+
+
+def query_service_sms_usage_for_year(service_id, year):
+    year_start, year_end = get_financial_year_dates(year)
+    chargeable_units = FactBilling.billable_units * FactBilling.rate_multiplier
+
+    # Subquery for the number of chargeable units in all rows preceding this one,
+    # which might be none if this is the first row (hence the "coalesce").
+    cumulative_chargeable_units = func.coalesce(
+        func.sum(chargeable_units).over(
+            order_by=[
+                FactBilling.bst_date,  # order is "ASC" by default
+                FactBilling.rate  # ensures test stability for rows on the same day
+            ],
+            rows=(None, -1)  # ROWS BETWEEN UNBOUNDED PRECEDING AND 1 ROW PRECEDING
+        ),
+        literal(0)
+    )
+
+    # Subquery for how much free allowance we have left before the current row,
+    # so we can work out the cost for this row after taking it into account.
+    cumulative_free_remainder = func.greatest(
+        AnnualBilling.free_sms_fragment_limit - cumulative_chargeable_units,
+        0
+    )
+
+    charged_units = func.greatest(
+        chargeable_units - cumulative_free_remainder,
+        literal(0)
+    ).cast(Integer)  # for some reason the result is a String!
+
+    free_chargeable_units = func.least(
+        cumulative_free_remainder,
+        chargeable_units,
+    ).cast(Integer)  # for some reason the result is a Decimal
+
+    return db.session.query(
+        FactBilling.bst_date,
+        FactBilling.postage,  # should always be "none"
+        FactBilling.notifications_sent,
+        # TEMPORARY: while we switch to "chargeable units"
+        chargeable_units.label("billable_units"),
+        chargeable_units.label("chargeable_units"),
+        FactBilling.rate,
+        FactBilling.notification_type,
+        charged_units.label("charged_units"),
+        free_chargeable_units.label("free_chargeable_units"),
+        (charged_units * FactBilling.rate).label("cost")
+    ).outerjoin(
+        AnnualBilling,
+        AnnualBilling.service_id == service_id
+    ).filter(
+        FactBilling.service_id == service_id,
+        FactBilling.bst_date >= year_start,
+        FactBilling.bst_date <= year_end,
+        FactBilling.notification_type == SMS_TYPE,
+        AnnualBilling.financial_year_start == year,
+    )
 
 
 def delete_billing_data_for_service_for_day(process_day, service_id):

tests/app/billing/test_rest.py

@@ -147,6 +147,8 @@ def set_up_monthly_data():
                               billable_unit=1,
                               rate=0.33,
                               postage='second')
+
+    create_annual_billing(service_id=service.id, free_sms_fragment_limit=4, financial_year_start=2016)
     return service
 
 
@@ -170,14 +172,25 @@ def test_get_yearly_usage_by_monthly_from_ft_billing(admin_request, notify_db_se
     assert letter_row["month"] == "April"
     assert letter_row["notification_type"] == "letter"
     assert letter_row["billing_units"] == 30
+    assert letter_row["chargeable_units"] == 30
     assert letter_row["rate"] == 0.33
     assert letter_row["postage"] == "second"
+    assert letter_row["cost"] == 9.9
+    assert letter_row["free_chargeable_units"] == 0
+    assert letter_row["charged_units"] == 30
+    assert letter_row["notifications_sent"] == 30
 
     assert sms_row["month"] == "April"
     assert sms_row["notification_type"] == "sms"
     assert sms_row["billing_units"] == 30
+    assert sms_row["chargeable_units"] == 30
     assert sms_row["rate"] == 0.162
     assert sms_row["postage"] == "none"
+    # free allowance is 4, so (30 - 4) * 0.162
+    assert sms_row["cost"] == 4.212
+    assert sms_row["free_chargeable_units"] == 4
+    assert sms_row["charged_units"] == 26
+    assert sms_row["notifications_sent"] == 30
 
 
 def set_up_yearly_data():
@@ -185,6 +198,7 @@ def set_up_yearly_data():
     sms_template = create_template(service=service, template_type="sms")
     email_template = create_template(service=service, template_type="email")
     letter_template = create_template(service=service, template_type="letter")
+
     for month in range(1, 13):
         mon = str(month).zfill(2)
         for day in range(1, monthrange(2016, month)[1] + 1):
@@ -205,6 +219,8 @@ def set_up_yearly_data():
                               rate=0.33,
                               postage='second')
         start_date, end_date = get_month_start_and_end_date_in_utc(datetime(2016, int(mon), 1))
+
+    create_annual_billing(service_id=service.id, free_sms_fragment_limit=4, financial_year_start=2016)
     return service
 
 
@@ -240,15 +256,33 @@ def test_get_yearly_billing_usage_summary_from_ft_billing(admin_request, notify_
     )
 
     assert len(json_response) == 3
+
     assert json_response[0]['notification_type'] == 'email'
     assert json_response[0]['billing_units'] == 275
+    assert json_response[0]['chargeable_units'] == 275
     assert json_response[0]['rate'] == 0
     assert json_response[0]['letter_total'] == 0
+    assert json_response[0]['cost'] == 0
+    assert json_response[0]['free_chargeable_units'] == 0
+    assert json_response[0]['charged_units'] == 275
+    assert json_response[0]['notifications_sent'] == 275
+
     assert json_response[1]['notification_type'] == 'letter'
     assert json_response[1]['billing_units'] == 275
+    assert json_response[1]['chargeable_units'] == 275
     assert json_response[1]['rate'] == 0.33
     assert json_response[1]['letter_total'] == 90.75
+    assert json_response[1]['cost'] == 90.75
+    assert json_response[1]['free_chargeable_units'] == 0
+    assert json_response[1]['charged_units'] == 275
+    assert json_response[1]['notifications_sent'] == 275
+
     assert json_response[2]['notification_type'] == 'sms'
     assert json_response[2]['billing_units'] == 825
+    assert json_response[2]['chargeable_units'] == 825
     assert json_response[2]['rate'] == 0.0162
     assert json_response[2]['letter_total'] == 0
+    assert json_response[2]['cost'] == 13.3002
+    assert json_response[2]['free_chargeable_units'] == 4
+    assert json_response[2]['charged_units'] == 821
+    assert json_response[2]['notifications_sent'] == 825

tests/app/dao/test_ft_billing_dao.py

@@ -417,6 +417,7 @@ def test_get_rate_for_letters_when_page_count_is_zero(notify_db_session):
 
 def test_fetch_monthly_billing_for_year(notify_db_session):
     service = set_up_yearly_data()
+    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
@@ -425,25 +426,42 @@ def test_fetch_monthly_billing_for_year(notify_db_session):
     assert results[0].notification_type == 'email'
     assert results[0].notifications_sent == 30
     assert results[0].billable_units == 30
+    assert results[0].chargeable_units == 30
     assert results[0].rate == Decimal('0')
+    assert results[0].cost == Decimal('0')
+    assert results[0].free_chargeable_units == 0
+    assert results[0].charged_units == 30
 
     assert str(results[1].month) == "2016-04-01"
     assert results[1].notification_type == 'letter'
     assert results[1].notifications_sent == 30
     assert results[1].billable_units == 30
+    assert results[1].chargeable_units == 30
     assert results[1].rate == Decimal('0.30')
+    assert results[1].cost == Decimal('9')
+    assert results[1].free_chargeable_units == 0
+    assert results[1].charged_units == 30
 
     assert str(results[1].month) == "2016-04-01"
     assert results[2].notification_type == 'letter'
     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_chargeable_units == 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')
+    # free allowance is 10, so (30 - 10) * 0.162
+    assert results[3].cost == Decimal('3.24')
+    assert results[3].free_chargeable_units == 10
+    assert results[3].charged_units == 20
 
     assert str(results[4].month) == "2016-05-01"
     assert str(results[47].month) == "2017-03-01"
@@ -451,6 +469,7 @@ def test_fetch_monthly_billing_for_year(notify_db_session):
 
 def test_fetch_monthly_billing_for_year_variable_rates(notify_db_session):
     service = set_up_yearly_data_variable_rates()
+    create_annual_billing(service_id=service.id, free_sms_fragment_limit=6, financial_year_start=2018)
     results = fetch_monthly_billing_for_year(service.id, 2018)
 
     # Test data is only for the month of May
@@ -460,25 +479,43 @@ def test_fetch_monthly_billing_for_year_variable_rates(notify_db_session):
     assert results[0].notification_type == 'letter'
     assert results[0].notifications_sent == 1
     assert results[0].billable_units == 1
+    assert results[0].chargeable_units == 1
     assert results[0].rate == Decimal('0.33')
+    assert results[0].cost == Decimal('0.33')
+    assert results[0].free_chargeable_units == 0
+    assert results[0].charged_units == 1
 
     assert str(results[1].month) == "2018-05-01"
     assert results[1].notification_type == 'letter'
     assert results[1].notifications_sent == 1
     assert results[1].billable_units == 1
+    assert results[1].chargeable_units == 2
     assert results[1].rate == Decimal('0.36')
+    assert results[1].cost == Decimal('0.36')
+    assert results[1].free_chargeable_units == 0
+    assert results[1].charged_units == 1
 
     assert str(results[2].month) == "2018-05-01"
     assert results[2].notification_type == 'sms'
     assert results[2].notifications_sent == 1
     assert results[2].billable_units == 4
+    assert results[2].chargeable_units == 4
     assert results[2].rate == Decimal('0.015')
+    # 4 free units sent on the 16th, 0 on the 17th
+    assert results[2].cost == Decimal('0')
+    assert results[2].free_chargeable_units == 4
+    assert results[2].charged_units == 0
 
     assert str(results[3].month) == "2018-05-01"
     assert results[3].notification_type == 'sms'
     assert results[3].notifications_sent == 2
     assert results[3].billable_units == 5
+    assert results[3].chargeable_units == 5
     assert results[3].rate == Decimal('0.162')
+    # 1 free unit on the 16th, 1 on the 17th (+ 3 paid)
+    assert results[3].cost == Decimal('0.486')
+    assert results[3].free_chargeable_units == 2
+    assert results[3].charged_units == 3
 
 
 @freeze_time('2018-08-01 13:30:00')
@@ -487,6 +524,7 @@ def test_fetch_monthly_billing_for_year_adds_data_for_today(notify_db_session):
     template = create_template(service=service, template_type="sms")
 
     create_rate(start_date=datetime.utcnow() - timedelta(days=1), value=0.158, notification_type='sms')
+    create_annual_billing(service_id=service.id, free_sms_fragment_limit=1000, financial_year_start=2018)
 
     for i in range(1, 32):
         create_ft_billing(bst_date='2018-07-{}'.format(i), template=template)
@@ -502,54 +540,105 @@ def test_fetch_monthly_billing_for_year_adds_data_for_today(notify_db_session):
 
 def test_fetch_billing_totals_for_year(notify_db_session):
     service = set_up_yearly_data()
+    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 results[0].notification_type == 'email'
     assert results[0].notifications_sent == 365
     assert results[0].billable_units == 365
+    assert results[0].chargeable_units == 365
     assert results[0].rate == Decimal('0')
+    assert results[0].cost == Decimal('0')
+    assert results[0].free_chargeable_units == 0
+    assert results[0].charged_units == 365
 
     assert results[1].notification_type == 'letter'
     assert results[1].notifications_sent == 365
     assert results[1].billable_units == 365
+    assert results[1].chargeable_units == 365
     assert results[1].rate == Decimal('0.3')
+    assert results[1].cost == Decimal('109.5')
+    assert results[1].free_chargeable_units == 0
+    assert results[1].charged_units == 365
 
     assert results[2].notification_type == 'letter'
     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_chargeable_units == 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_chargeable_units == 365
+    assert results[3].charged_units == 0
+
+
+def test_fetch_billing_totals_for_year_uses_current_annual_billing(notify_db_session):
+    service = set_up_yearly_data()
+    create_annual_billing(service_id=service.id, free_sms_fragment_limit=400, financial_year_start=2015)
+    create_annual_billing(service_id=service.id, free_sms_fragment_limit=0, financial_year_start=2016)
+
+    result = next(
+        result for result in
+        fetch_billing_totals_for_year(service_id=service.id, year=2016)
+        if result.notification_type == 'sms'
+    )
+
+    assert result.chargeable_units == 365
+    assert result.cost > 0
 
 
 def test_fetch_billing_totals_for_year_variable_rates(notify_db_session):
     service = set_up_yearly_data_variable_rates()
+    create_annual_billing(service_id=service.id, free_sms_fragment_limit=6, financial_year_start=2018)
     results = fetch_billing_totals_for_year(service_id=service.id, year=2018)
 
     assert len(results) == 4
     assert results[0].notification_type == 'letter'
     assert results[0].notifications_sent == 1
     assert results[0].billable_units == 1
+    assert results[0].chargeable_units == 1
     assert results[0].rate == Decimal('0.33')
+    assert results[0].cost == Decimal('0.33')
+    assert results[0].free_chargeable_units == 0
+    assert results[0].charged_units == 1
 
     assert results[1].notification_type == 'letter'
     assert results[1].notifications_sent == 1
     assert results[1].billable_units == 1
+    assert results[1].chargeable_units == 2
     assert results[1].rate == Decimal('0.36')
+    assert results[1].cost == Decimal('0.36')
+    assert results[1].free_chargeable_units == 0
+    assert results[1].charged_units == 1
 
     assert results[2].notification_type == 'sms'
     assert results[2].notifications_sent == 1
     assert results[2].billable_units == 4
+    assert results[2].chargeable_units == 4
     assert results[2].rate == Decimal('0.015')
+    # 4 units sent on the 16th, 0 on the 17th
+    assert results[2].cost == Decimal('0')
+    assert results[2].free_chargeable_units == 4
+    assert results[2].charged_units == 0
 
     assert results[3].notification_type == 'sms'
     assert results[3].notifications_sent == 2
     assert results[3].billable_units == 5
+    assert results[3].chargeable_units == 5
     assert results[3].rate == Decimal('0.162')
+    # 1 free unit on the 16th, 1 on the 17th (+ 3 paid)
+    assert results[3].cost == Decimal('0.486')  # (5 - 2) * 0.162
+    assert results[3].free_chargeable_units == 2
+    assert results[3].charged_units == 3
 
 
 def test_delete_billing_data(notify_db_session):