Refactor sending methods to use error mappers

We want to add some logic to error handling.
This commit extracts error handling code from sending methods classes,
which already do a lot of other stuff, to error mappers which are responsible
for creating proper error object (MailerError). This error object is a replacement
for assoc. array which already had some special keys for certain usecases and
can not be properly type hinted.

[MAILPOET-1154]

tests/unit/Mailer/Methods/ErrorMappers/SMTPMapperTest.php

@@ -0,0 +1,46 @@
+<?php
+namespace MailPoet\Test\Mailer\Methods\ErrorMappers;
+
+use MailPoet\Mailer\Mailer;
+use MailPoet\Mailer\Methods\ErrorMappers\SMTPMapper;
+
+class SMTPMapperTest extends \MailPoetTest {
+
+  /** @var SMTPMapper */
+  private $mapper;
+
+  function _before() {
+    $this->mapper = new SMTPMapper();
+  }
+
+  function testItCanProcessExceptionMessage() {
+    $message = 'Connection could not be established with host localhost [Connection refused #111]' . PHP_EOL
+      . 'Log data:' . PHP_EOL
+      . '++ Starting Swift_SmtpTransport' . PHP_EOL
+      . '!! Connection could not be established with host localhost [Connection refused #111] (code: 0)';
+    $error = $this->mapper->getErrorFromException(new \Exception($message));
+    expect($error->getMessage())
+      ->equals('Connection could not be established with host localhost [Connection refused #111]');
+  }
+
+  function testItCanProcessLogMessageWhenOneExists() {
+    $log = '++ Swift_SmtpTransport started' . PHP_EOL
+      . '>> MAIL FROM:<moi@mrcasual.com>' . PHP_EOL
+      . '<< 250 OK' . PHP_EOL
+      . '>> RCPT TO:<test2@ietsdoenofferte.nl>' . PHP_EOL
+      . '<< 550 No such recipient here' . PHP_EOL
+      . '!! Expected response code 250/251/252 but got code "550", with message "550 No such recipient here' . PHP_EOL
+      . '" (code: 550)' . PHP_EOL
+      . '>> RSET' . PHP_EOL
+      . '<< 250 Reset OK' . PHP_EOL;
+    $error = $this->mapper->getErrorFromLog($log, 'test@example.com', []);
+    expect($error->getMessage())
+      ->equals('Expected response code 250/251/252 but got code "550", with message "550 No such recipient here" (code: 550) Unprocessed subscriber: test@example.com');
+  }
+
+  function testItReturnsGenericMessageWhenLogMessageDoesNotExist() {
+    $error = $this->mapper->getErrorFromLog(null, 'test@example.com');
+    expect($error->getMessage())
+      ->equals(Mailer::METHOD_SMTP . ' has returned an unknown error. Unprocessed subscriber: test@example.com');
+  }
+}