Add referral id URL decorator

[MAILPOET-2182]

tests/integration/Referrals/UrlDecoratorTest.php

@@ -0,0 +1,37 @@
+<?php
+namespace MailPoet\Test\Router;
+
+use MailPoet\Referrals\ReferralDetector;
+use MailPoet\Referrals\UrlDecorator;
+use MailPoet\Settings\SettingsController;
+use MailPoet\WP\Functions as WPFunctions;
+
+class UrlDecoratorTest extends \MailPoetTest {
+  /** @var SettingsController */
+  private $settings;
+
+  /** @var UrlDecorator */
+  private $url_decorator;
+
+  function _before() {
+    parent::_before();
+    $this->settings = new SettingsController();
+    $this->url_decorator = new UrlDecorator(WPFunctions::get(), $this->settings);
+  }
+
+  function testItDoesntDoAnythingWhenNoReferralId() {
+    $this->settings->set(ReferralDetector::REFERRAL_SETTING_NAME, null);
+    $url = 'http://example.com';
+    expect($this->url_decorator->decorate($url))->equals($url);
+  }
+
+  function testItCorrectlyAddsReferralId() {
+    $this->settings->set(ReferralDetector::REFERRAL_SETTING_NAME, 'abcdefgh');
+    expect($this->url_decorator->decorate('http://example.com/'))
+      ->equals('http://example.com/?ref=abcdefgh');
+    expect($this->url_decorator->decorate('http://example.com/?param=value'))
+      ->equals('http://example.com/?param=value&ref=abcdefgh');
+    expect($this->url_decorator->decorate('http://example.com/?param=value#hash/?param=val'))
+      ->equals('http://example.com/?param=value&ref=abcdefgh#hash/?param=val');
+  }
+}