Testing if email was sent in Kernel test I am trying to write automated tests for a or that will sent an email on submission.
I can write the test to check for the presence of the entity that is created along side the email, but I also want to have my automated test check that the system is sending an email too.
The examples I can find seem to relate to Laravel and the use of spies to see if a particular class method is called, however I can't find any examples of how to do that in Drupal 8 and in my particular use case I am using the function _user_mail_notify() and not a class method.
Does anyone have an example of testing that emails have seen sent at all?
Look at core tests that utilize email. For example:

MailCaptureTest::testMailSend()
EmailActionTest::testEmailAction()

The tests demonstrate ways to inspect the plugin.manager.mail service for signs that mail was successfully sent.