PHPUnit test for method that sends email once - php

Question

I am trying to write some unit test where I can check if creator of a post should not receive same email twice.
I am new at testing (not new in Symfony.) I tried some basic test and they work.
First of the problem is that this is a method inside of and DataPersister class within Api Platform which is called everytime entity is persisted and it sends an email to a user..
final class EmailDataPersister
{
public function persist($data, array $context = [])
{
$result = $this->decorated->persist($data, $context);
if (
$data instanceof User&& (
($context['collection_operation_name'] ?? null) === 'post')
) {
$this->sendEmail($data);
}
return $result;
}
private function sendEmail(User $user)
{
$email = (new EmailNotification())
->setTitle('Hello ' . $user->getName())
->setFrom('sender#sent.com')
->setAddress($user->getEmail)
->setBody('This is a new email');
$this->messageBus->dispatch($email);
}
}
Tried something like:
class someModelTest extends TestCase
public function testEmails()
{
$this->satEmail('test#pmg.co');
$this->assertMessageCount(1, 'should have sent one email');
$msg = $this->getMessages()[0];
$this->assertArrayHasKey('test#pmg.co', $msg->getTo());
}
public function satEmail($email)
{
$msg = (new \Swift_Message('Testing..'))
->setSubject('Hello')
->setBody('Hello')
->setFrom('helle#example.com')
->setTo($email);
$this->mailer->send($msg);
}
I think I need to add..
$model = $this->getMock('someModel', array('setFrom', 'setTo', 'setSubject', 'send'));
$controller->expects($this->once())
->method('setFrom');
$controller->expects($this->once())
->method('setTo');
$controller->expects($this->once())
->method('setSubject');
$controller->expects($this->once())
->method('send');
$model->sendEmail();
}
I can not figure out should I call that method inside the class or what should I define model controller etc?