diff --git a/facets.plugin_type.yml b/facets.plugin_type.yml
index 1fd9cbf..8db8901 100644
--- a/facets.plugin_type.yml
+++ b/facets.plugin_type.yml
@@ -3,6 +3,11 @@ facets_processor:
   plugin_manager_service_id: plugin.manager.facets.processor
   plugin_definition_decorator_class: \Drupal\plugin\PluginDefinition\ArrayPluginDefinitionDecorator
 
+facets_url_processor:
+  label: Facets URL processor
+  plugin_manager_service_id: plugin.manager.facets.url_processor
+  plugin_definition_decorator_class: \Drupal\plugin\PluginDefinition\ArrayPluginDefinitionDecorator
+
 facets_facet_source:
   label: Facets source
   plugin_manager_service_id: plugin.manager.facets.facet_source
diff --git a/src/Entity/FacetSource.php b/src/Entity/FacetSource.php
index 14c792e..0ed4cc8 100644
--- a/src/Entity/FacetSource.php
+++ b/src/Entity/FacetSource.php
@@ -77,13 +77,6 @@ class FacetSource extends ConfigEntityBase implements FacetSourceInterface {
   protected $urlProcessor = 'query_string';
 
   /**
-   * The url processor instance.
-   *
-   * @var \Drupal\facets\UrlProcessor\UrlProcessorInterface
-   */
-  protected $urlProcessorInstance = NULL;
-
-  /**
    * {@inheritdoc}
    */
   public function id() {
diff --git a/src/Form/FacetSourceEditForm.php b/src/Form/FacetSourceEditForm.php
index 1eaba54..bdc7779 100644
--- a/src/Form/FacetSourceEditForm.php
+++ b/src/Form/FacetSourceEditForm.php
@@ -33,13 +33,13 @@ class FacetSourceEditForm extends EntityForm {
    * {@inheritdoc}
    */
   public static function create(ContainerInterface $container) {
-    /** @var \Drupal\Core\Entity\EntityTypeManagerInterface $etm */
-    $etm = $container->get('entity_type.manager');
+    /** @var \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager */
+    $entity_type_manager = $container->get('entity_type.manager');
 
-    /** @var \Drupal\facets\UrlProcessor\UrlProcessorPluginManager $uppm */
-    $uppm = $container->get('plugin.manager.facets.url_processor');
+    /** @var \Drupal\facets\UrlProcessor\UrlProcessorPluginManager $url_processor_plugin_manager */
+    $url_processor_plugin_manager = $container->get('plugin.manager.facets.url_processor');
 
-    return new static($etm, $uppm);
+    return new static($entity_type_manager, $url_processor_plugin_manager);
   }
 
   /**
diff --git a/src/Tests/UrlIntegrationTest.php b/src/Tests/UrlIntegrationTest.php
index 62339d3..565392e 100644
--- a/src/Tests/UrlIntegrationTest.php
+++ b/src/Tests/UrlIntegrationTest.php
@@ -32,20 +32,26 @@ class UrlIntegrationTest extends FacetWebTestBase {
   ];
 
   /**
-   * Tests various url integration things.
+   * {@inheritdoc}
    */
-  public function testUrlIntegration() {
+  public function setUp() {
+    parent::setUp();
+
     $this->drupalLogin($this->adminUser);
 
     $this->insertExampleContent();
     $this->assertEqual($this->indexItems($this->indexId), 5, '5 items were indexed.');
+  }
 
+  /**
+   * Tests various url integration things.
+   */
+  public function testUrlIntegration() {
     $id = 'facet';
     $name = '&^Facet@#1';
-
     $facet_add_page = 'admin/config/search/facets/add-facet';
+
     $this->drupalGet($facet_add_page);
-    $this->assertResponse(200);
 
     $form_values = [
       'id' => $id,
@@ -57,47 +63,38 @@ class UrlIntegrationTest extends FacetWebTestBase {
     ];
     $this->drupalPostForm(NULL, ['facet_source_id' => 'search_api_views:search_api_test_views_fulltext:page_1'], $this->t('Configure facet source'));
     $this->drupalPostForm(NULL, $form_values, $this->t('Save'));
-    $this->assertNoText('field is required.');
-
-    $this->assertRaw(t('Facet %name has been created.', ['%name' => $name]));
 
+    // Go to the only enabled facet source's config.
     $this->drupalGet('admin/config/search/facets');
+    $this->clickLink($this->t('Configure'));
 
     $edit = [
       'filterKey' => 'y',
       'urlProcessor' => 'dummy_query',
     ];
-    $this->clickLink($this->t('Configure'));
     $this->drupalPostForm(NULL, $edit, $this->t('Save'));
 
     /** @var \Drupal\facets\FacetInterface $facet */
     $facet = \Drupal::service('entity_type.manager')->getStorage('facets_facet')->load($id);
     $block_values = [
-      [
-        'label' => 'Facet Block',
-        'tr' => '16',
-        'plugin_id' => 'facet_block',
-        'settings' => [
-          'region' => 'footer',
-          'id' => str_replace('_', '-', $id),
-          'context_mapping' => [
-            'facet' => '@facets.facet_context:' . $facet->uuid(),
-          ],
-        ],
-        'test_weight' => '0',
+      'region' => 'footer',
+      'id' => str_replace('_', '-', $id),
+      'context_mapping' => [
+        'facet' => '@facets.facet_context:' . $facet->uuid(),
       ],
     ];
-    foreach ($block_values as $values) {
-      $this->drupalPlaceBlock($values['plugin_id'], $values['settings']);
-    }
+    $this->drupalPlaceBlock('facet_block', $block_values);
 
     $this->drupalGet('search-api-test-fulltext');
+    $this->assertResponse(200);
     $this->assertLink('item');
     $this->assertLink('article');
 
     $this->clickLink('item');
 
+    $this->assertResponse(200);
     $this->assertLink('(-) item');
+    $this->assertNoLink('article');
     $this->assertUrl('search-api-test-fulltext?y[0]=facet||item');
   }
 
diff --git a/src/UrlProcessor/UrlProcessorInterface.php b/src/UrlProcessor/UrlProcessorInterface.php
index e040db4..3bc51a1 100644
--- a/src/UrlProcessor/UrlProcessorInterface.php
+++ b/src/UrlProcessor/UrlProcessorInterface.php
@@ -22,8 +22,27 @@ use Drupal\facets\FacetInterface;
  */
 interface UrlProcessorInterface {
 
+  /**
+   * Adds urls to the results.
+   *
+   * @param \Drupal\facets\FacetInterface $facet
+   *   The facet.
+   * @param \Drupal\facets\Result\ResultInterface[] $results
+   *   An array of results.
+   *
+   * @return \Drupal\facets\Result\ResultInterface[]
+   *   An array of results with added urls.
+   */
   public function buildUrls(FacetInterface $facet, array $results);
 
+  /**
+   * Sets active items.
+   *
+   * Makes sure that the items that are already set in the current request are
+   * remembered when building the facet's urls.
+   *
+   * @param \Drupal\facets\FacetInterface $facet
+   */
   public function setActiveItems(FacetInterface $facet);
 
   /**
diff --git a/src/UrlProcessor/UrlProcessorPluginManager.php b/src/UrlProcessor/UrlProcessorPluginManager.php
index d3f3dcf..84008fd 100644
--- a/src/UrlProcessor/UrlProcessorPluginManager.php
+++ b/src/UrlProcessor/UrlProcessorPluginManager.php
@@ -11,7 +11,6 @@ use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\Plugin\DefaultPluginManager;
 use Drupal\Core\StringTranslation\StringTranslationTrait;
-use Drupal\Core\StringTranslation\TranslationInterface;
 
 /**
  * Manages URL processor plugins.
diff --git a/tests/src/Unit/Plugin/url_processor/QueryStringTest.php b/tests/src/Unit/Plugin/url_processor/QueryStringTest.php
index 9698c84..df418fb 100644
--- a/tests/src/Unit/Plugin/url_processor/QueryStringTest.php
+++ b/tests/src/Unit/Plugin/url_processor/QueryStringTest.php
@@ -55,6 +55,14 @@ class QueryStringTest extends UnitTestCase {
   }
 
   /**
+   * Tests that the processor correctly throws an exception.
+   */
+  public function testEmptyProcessorConfiguration() {
+    $this->setExpectedException('\Drupal\facets\Exception\InvalidProcessorException', "The url processor doesn't have the required 'facet' in the configuration array.");
+    new QueryString([], 'test', [], new Request());
+  }
+
+  /**
    * Basic test with one active item.
    */
   public function testSetSingleActiveItem() {