Writing services that are testable

testable-service-good.py

from .auth import AccessControlList

class GoodBookService(object):
  def __init__(self, acl_service=AccessControlList()):
    self.acl = acl_service
    
   def create_book(self, user, book):
    if self.acl.can_create_book(user):
      # ... code to create book
     else:
      # ... raise an exception