In the process it was necessary to change the signature of the method
\MailPoet\Mailer\MetaInfo::getNewsletterMetaInfo() to accept a
SubscriberEntity instead of a Subscriber model and also change
\MailPoet\Cron\Workers\SendingQueue\SendingQueue::processQueue() as it
calls getNewsletterMetaInfo().
Doing this was straightforward, but changing the test class for
SendingQueue was a bit more involved. In particular, the test
SendingQueueTest::testItEnforcesExecutionLimitsAfterQueueProcessing().
This test is a bit brittle and was creating Subscriber models without
saving them to the database with invalid statuses and sources. Switching
getNewsletterMetaInfo() to use entities, while
SendingQueue::processQueue() still uses models, meant that it was
necessary to save the subscribers to the database. Because of this, it
was not possible anymore to use invalid statuses and sources, and
thus, the test changed a bit.
[MAILPOET-4379]
