Implementation of automated testing

It would be great to add automated testing to the module.

Test cases

Checkbox:
The checkbox should be displayed on two blocks "simplenews_block_form" and "simplenews_subscriptions_multi_block_form".
The checkbox doesn't need to be displayed on "simplenews_subscriptions_multi_block_form" if the user already subscribed all visible newsletters.

Data:
Anonymous users do not need data to be recorded on the db.
For registered users we are saving the tid and the uid.