MailerHandler example

class MailerHandlerTest extends TestCase
{
    private MockObject&MailerInterface $mailer;

    protected function setUp(): void
    {
        $this->mailer = $this->createMock(MailerInterface::class);
    }

    public function testHandle()
    {
        $handler = new MailerHandler($this->mailer, (new Email())->subject('Alert: %level_name% %message%'));
        $handler->setFormatter(new LineFormatter());
        $this->mailer
            ->expects($this->once())
            ->method('send')
            ->with($this->callback(fn (Email $email) => 'Alert: WARNING message' === $email->getSubject() && null === $email->getHtmlBody()))
        ;
        $handler->handle($this->getRecord(Logger::WARNING, 'message'));
    }

    public function testHandleBatch()
    {