Store anticipated volumes as integers

This will make it easier to do analysis on the data. Almost all users
are submitting data in a numerical format now anyway, because we ask the
question in a sensible way.

app/models.py

@@ -361,9 +361,9 @@ class Service(db.Model, Versioned):
     crown = db.Column(db.Boolean, index=False, nullable=False, default=True)
     rate_limit = db.Column(db.Integer, index=False, nullable=False, default=3000)
     contact_link = db.Column(db.String(255), nullable=True, unique=False)
-    volume_sms = db.Column(db.String(255), nullable=True, unique=False)
-    volume_email = db.Column(db.String(255), nullable=True, unique=False)
-    volume_letter = db.Column(db.String(255), nullable=True, unique=False)
+    volume_sms = db.Column(db.Integer(), nullable=True, unique=False)
+    volume_email = db.Column(db.Integer(), nullable=True, unique=False)
+    volume_letter = db.Column(db.Integer(), nullable=True, unique=False)
 
     organisation = db.relationship(
         'Organisation',

migrations/versions/0260_service_volumes.py

@@ -22,7 +22,7 @@ TABLES_AND_CHANNELS = product(
 
 def upgrade():
     for table, channel in TABLES_AND_CHANNELS:
-        op.add_column(table, sa.Column(channel, sa.String(length=255), nullable=True))
+        op.add_column(table, sa.Column(channel, sa.Integer(), nullable=True))
 
 
 def downgrade():

tests/app/service/test_rest.py

@@ -620,15 +620,18 @@ def test_update_service_sets_crown(client, sample_service, org_type, expected):
     'volume_sms',
     'volume_letter',
 ))
-@pytest.mark.parametrize('value', (
-    'ABC123',
-    None,
+@pytest.mark.parametrize('value, expected_status, expected_persisted', (
+    (1234, 200, 1234),
+    (None, 200, None),
+    ('Aa', 400, None),
 ))
 def test_update_service_sets_volumes(
     admin_request,
     sample_service,
     field,
     value,
+    expected_status,
+    expected_persisted,
 ):
     admin_request.post(
         'service.update_service',
@@ -636,9 +639,9 @@ def test_update_service_sets_volumes(
         _data={
             field: value,
         },
-        _expected_status=200,
+        _expected_status=expected_status,
     )
-    assert getattr(sample_service, field) == value
+    assert getattr(sample_service, field) == expected_persisted
 
 
 @pytest.fixture(scope='function')