Validate length of broadcast templates on creation

This is a belt-and-braces check because the admin app already checks
this. But since we do it for SMS already it makes sense to replicate it
for broadcast templates.

app/template/rest.py

@@ -5,7 +5,10 @@ import botocore
 from flask import Blueprint, current_app, jsonify, request
 from notifications_utils import SMS_CHAR_COUNT_LIMIT
 from notifications_utils.pdf import extract_page_from_pdf
-from notifications_utils.template import SMSMessageTemplate
+from notifications_utils.template import (
+    BroadcastMessageTemplate,
+    SMSMessageTemplate,
+)
 from PyPDF2.utils import PdfReadError
 from requests import post as requests_post
 from sqlalchemy.orm.exc import NoResultFound
@@ -28,7 +31,13 @@ from app.dao.templates_dao import (
 )
 from app.errors import InvalidRequest, register_errors
 from app.letters.utils import get_letter_pdf_and_metadata
-from app.models import LETTER_TYPE, SECOND_CLASS, SMS_TYPE, Template
+from app.models import (
+    BROADCAST_TYPE,
+    LETTER_TYPE,
+    SECOND_CLASS,
+    SMS_TYPE,
+    Template,
+)
 from app.notifications.validators import check_reply_to, service_has_permission
 from app.schema_validation import validate
 from app.schemas import (
@@ -48,10 +57,13 @@ register_errors(template_blueprint)
 
 
 def _content_count_greater_than_limit(content, template_type):
-    if template_type != SMS_TYPE:
+    if template_type == SMS_TYPE:
-        return False
+        template = SMSMessageTemplate({'content': content, 'template_type': template_type})
-    template = SMSMessageTemplate({'content': content, 'template_type': template_type})
+        return template.is_message_too_long()
-    return template.is_message_too_long()
+    if template_type == BROADCAST_TYPE:
+        template = BroadcastMessageTemplate({'content': content, 'template_type': template_type})
+        return template.is_message_too_long()
+    return False
 
 
 def validate_parent_folder(template_json):

tests/app/template/test_rest.py

@@ -731,14 +731,24 @@ def test_should_return_404_if_no_templates_for_service_with_id(client, sample_se
     assert json_resp['message'] == 'No result found'
 
 
-def test_create_400_for_over_limit_content(client, notify_api, sample_user, sample_service, fake_uuid):
+@pytest.mark.parametrize('template_type', (
+    SMS_TYPE, BROADCAST_TYPE,
+))
+def test_create_400_for_over_limit_content(
+    client,
+    notify_api,
+    sample_user,
+    fake_uuid,
+    template_type,
+):
+    sample_service = create_service(service_permissions=[template_type])
     content = ''.join(random.choice(string.ascii_uppercase + string.digits) for _ in range(SMS_CHAR_COUNT_LIMIT + 1))
     data = {
         'name': 'too big template',
-        'template_type': SMS_TYPE,
+        'template_type': template_type,
         'content': content,
         'service': str(sample_service.id),
-        'created_by': str(sample_user.id)
+        'created_by': str(sample_service.created_by.id)
     }
     data = json.dumps(data)
     auth_header = create_authorization_header()