diff --git a/core/modules/update/lib/Drupal/update/UpdateFetcher.php b/core/modules/update/lib/Drupal/update/UpdateFetcher.php
index f1600a7..047ef0e 100644
--- a/core/modules/update/lib/Drupal/update/UpdateFetcher.php
+++ b/core/modules/update/lib/Drupal/update/UpdateFetcher.php
@@ -14,7 +14,7 @@
 /**
  * Fetches project information from remote locations.
  */
-class UpdateFetcher {
+class UpdateFetcher implements UpdateFetcherInterface {
 
   /**
    * URL to check for updates, if a given project doesn't define its own.
@@ -57,15 +57,7 @@ public function __construct(ConfigFactory $config_factory, ClientInterface $http
   }
 
   /**
-   * Retrieves the project information.
-   *
-   * @param array $project
-   *   The array of project information from update_get_projects().
-   * @param string $site_key
-   *   (optional) The anonymous site key hash. Defaults to an empty string.
-   *
-   * @return string
-   *   The project information fetched as string. Empty string upon failure.
+   * {@inheritdoc}
    */
   public function fetchProjectData(array $project, $site_key = '') {
     $url = $this->buildFetchUrl($project, $site_key);
@@ -83,23 +75,7 @@ public function fetchProjectData(array $project, $site_key = '') {
   }
 
   /**
-   * Generates the URL to fetch information about project updates.
-   *
-   * This figures out the right URL to use, based on the project's .info.yml file
-   * and the global defaults. Appends optional query arguments when the site is
-   * configured to report usage stats.
-   *
-   * @param array $project
-   *   The array of project information from update_get_projects().
-   * @param string $site_key
-   *   (optional) The anonymous site key hash. Defaults to an empty string.
-   *
-   * @return string
-   *   The URL for fetching information about updates to the specified project.
-   *
-   * @see \Drupal\update\UpdateProcessor::fetchData()
-   * @see \Drupal\update\UpdateProcessor::processFetchTask()
-   * @see \Drupal\update\UpdateManager::getProjects()
+   * {@inheritdoc}
    */
   public function buildFetchUrl(array $project, $site_key = '') {
     $name = $project['name'];
@@ -129,15 +105,7 @@ public function buildFetchUrl(array $project, $site_key = '') {
   }
 
   /**
-   * Returns the base of the URL to fetch available update data for a project.
-   *
-   * @param array $project
-   *   The array of project information from update_get_projects().
-   *
-   * @return string
-   *   The base of the URL used for fetching available update data. This does
-   *   not include the path elements to specify a particular project, version,
-   *   site_key, etc.
+   * {@inheritdoc}
    */
   public function getFetchBaseUrl($project) {
     if (isset($project['info']['project status url'])) {
diff --git a/core/modules/update/lib/Drupal/update/UpdateFetcherInterface.php b/core/modules/update/lib/Drupal/update/UpdateFetcherInterface.php
new file mode 100644
index 0000000..8ace958
--- /dev/null
+++ b/core/modules/update/lib/Drupal/update/UpdateFetcherInterface.php
@@ -0,0 +1,60 @@
+<?php
+/**
+ * @file
+ * Contains \Drupal\update\UpdateFetcherInterface.
+ */
+
+namespace Drupal\update;
+
+/**
+ * Fetches project information from remote locations.
+ */
+interface UpdateFetcherInterface {
+
+  /**
+   * Returns the base of the URL to fetch available update data for a project.
+   *
+   * @param array $project
+   *   The array of project information from update_get_projects().
+   *
+   * @return string
+   *   The base of the URL used for fetching available update data. This does
+   *   not include the path elements to specify a particular project, version,
+   *   site_key, etc.
+   */
+  public function getFetchBaseUrl($project);
+
+  /**
+   * Retrieves the project information.
+   *
+   * @param array $project
+   *   The array of project information from update_get_projects().
+   * @param string $site_key
+   *   (optional) The anonymous site key hash. Defaults to an empty string.
+   *
+   * @return string
+   *   The project information fetched as string. Empty string upon failure.
+   */
+  public function fetchProjectData(array $project, $site_key = '');
+
+  /**
+   * Generates the URL to fetch information about project updates.
+   *
+   * This figures out the right URL to use, based on the project's .info.yml
+   * file and the global defaults. Appends optional query arguments when the
+   * site is configured to report usage stats.
+   *
+   * @param array $project
+   *   The array of project information from update_get_projects().
+   * @param string $site_key
+   *   (optional) The anonymous site key hash. Defaults to an empty string.
+   *
+   * @return string
+   *   The URL for fetching information about updates to the specified project.
+   *
+   * @see \Drupal\update\UpdateProcessor::fetchData()
+   * @see \Drupal\update\UpdateProcessor::processFetchTask()
+   * @see \Drupal\update\UpdateManager::getProjects()
+   */
+  public function buildFetchUrl(array $project, $site_key = '');
+}
diff --git a/core/modules/update/lib/Drupal/update/UpdateManager.php b/core/modules/update/lib/Drupal/update/UpdateManager.php
index 6129e76..f82a55c 100644
--- a/core/modules/update/lib/Drupal/update/UpdateManager.php
+++ b/core/modules/update/lib/Drupal/update/UpdateManager.php
@@ -34,7 +34,7 @@ class UpdateManager {
   /**
    * Update Processor Service.
    *
-   * @var \Drupal\update\UpdateProcessor
+   * @var \Drupal\update\UpdateProcessorInterface
    */
   protected $updateProcessor;
 
@@ -73,14 +73,14 @@ class UpdateManager {
    *   The config factory.
    * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
    *   The Module Handler service
-   * @param \Drupal\update\UpdateProcessor $update_processor
+   * @param \Drupal\update\UpdateProcessorInterface $update_processor
    *   The Update Processor service.
    * @param \Drupal\Core\StringTranslation\TranslationInterface $translation
    *   The translation service.
    * @param \Drupal\Core\KeyValueStore\KeyValueFactoryInterface $key_value_expirable_factory
    *   The expirable key/value factory.
    */
-  public function __construct(ConfigFactory $config_factory, ModuleHandlerInterface $module_handler, UpdateProcessor $update_processor, TranslationInterface $translation, KeyValueFactoryInterface $key_value_expirable_factory) {
+  public function __construct(ConfigFactory $config_factory, ModuleHandlerInterface $module_handler, UpdateProcessorInterface $update_processor, TranslationInterface $translation, KeyValueFactoryInterface $key_value_expirable_factory) {
     $this->updateSettings = $config_factory->get('update.settings');
     $this->moduleHandler = $module_handler;
     $this->updateProcessor = $update_processor;
diff --git a/core/modules/update/lib/Drupal/update/UpdateProcessor.php b/core/modules/update/lib/Drupal/update/UpdateProcessor.php
index 0237fda..f9a5018 100644
--- a/core/modules/update/lib/Drupal/update/UpdateProcessor.php
+++ b/core/modules/update/lib/Drupal/update/UpdateProcessor.php
@@ -16,7 +16,7 @@
 /**
  * Process project update information.
  */
-class UpdateProcessor {
+class UpdateProcessor implements UpdateProcessorInterface {
 
   /**
    * The update settings
@@ -28,7 +28,7 @@ class UpdateProcessor {
   /**
    * The UpdateFetcher service.
    *
-   * @var \Drupal\update\UpdateFetcher
+   * @var \Drupal\update\UpdateFetcherInterface
    */
   protected $updateFetcher;
 
@@ -88,7 +88,7 @@ class UpdateProcessor {
    *   The config factory.
    * @param \Drupal\Core\Queue\QueueFactory $queue_factory
    *   The queue factory
-   * @param \Drupal\update\UpdateFetcher $update_fetcher
+   * @param \Drupal\update\UpdateFetcherInterface $update_fetcher
    *   The update fetcher service
    * @param \Drupal\Core\KeyValueStore\StateInterface $state_store
    *   The state service.
@@ -99,7 +99,7 @@ class UpdateProcessor {
    * @param \Drupal\Core\KeyValueStore\KeyValueFactoryInterface $key_value_expirable_factory
    *   The expirable key/value factory.
    */
-  public function __construct(ConfigFactory $config_factory, QueueFactory $queue_factory, UpdateFetcher $update_fetcher, StateInterface $state_store, PrivateKey $private_key, KeyValueFactoryInterface $key_value_factory, KeyValueFactoryInterface $key_value_expirable_factory) {
+  public function __construct(ConfigFactory $config_factory, QueueFactory $queue_factory, UpdateFetcherInterface $update_fetcher, StateInterface $state_store, PrivateKey $private_key, KeyValueFactoryInterface $key_value_factory, KeyValueFactoryInterface $key_value_expirable_factory) {
     $this->updateFetcher = $update_fetcher;
     $this->updateSettings = $config_factory->get('update.settings');
     $this->fetchQueue = $queue_factory->get('update_fetch_tasks');
diff --git a/core/modules/update/lib/Drupal/update/UpdateProcessorInterface.php b/core/modules/update/lib/Drupal/update/UpdateProcessorInterface.php
new file mode 100644
index 0000000..d41a57e
--- /dev/null
+++ b/core/modules/update/lib/Drupal/update/UpdateProcessorInterface.php
@@ -0,0 +1,84 @@
+<?php
+/**
+ * @file
+ * Contains \Drupal\update\UpdateProcessorInterface.
+ */
+
+namespace Drupal\update;
+
+
+/**
+ * Processor of project update information.
+ */
+interface UpdateProcessorInterface {
+
+  /**
+   * Claims an item in the update fetch queue for processing.
+   *
+   * @return bool|\stdClass
+   *   On success we return an item object. If the queue is unable to claim an
+   *   item it returns false.
+   *
+   * @see \Drupal\Core\Queue\QueueInterface::claimItem()
+   */
+  public function claimQueueItem();
+
+  /**
+   * Attempts to drain the queue of tasks for release history data to fetch.
+   */
+  public function fetchData();
+
+  /**
+   * Adds a task to the queue for fetching release history data for a project.
+   *
+   * We only create a new fetch task if there's no task already in the queue for
+   * this particular project (based on 'update_fetch_task' key-value
+   * collection).
+   *
+   * @param array $project
+   *   Associative array of information about a project as created by
+   *   update_get_projects(), including keys such as 'name' (short name), and
+   *   the 'info' array with data from a .info.yml file for the project.
+   *
+   * @see \Drupal\update\UpdateManager::getProjects()
+   * @see update_get_available()
+   * @see \Drupal\update\UpdateManager::refreshUpdateData()
+   * @see \Drupal\update\UpdateProcessor::fetchData()
+   * @see \Drupal\update\UpdateProcessor::processFetchTask()
+   */
+  public function createFetchTask($project);
+
+  /**
+   * Processes a task to fetch available update data for a single project.
+   *
+   * Once the release history XML data is downloaded, it is parsed and saved in
+   * an entry just for that project.
+   *
+   * @param array $project
+   *   Associative array of information about the project to fetch data for.
+   *
+   * @return bool
+   *   TRUE if we fetched parsable XML, otherwise FALSE.
+   */
+  public function processFetchTask($project);
+
+  /**
+   * Retrieves the number of items in the update fetch queue.
+   *
+   * @return int
+   *   An integer estimate of the number of items in the queue.
+   *
+   * @see \Drupal\Core\Queue\QueueInterface::numberOfItems()
+   */
+  public function numberOfQueueItems();
+
+  /**
+   * Deletes a finished item from the update fetch queue.
+   *
+   * @param \stdClass $item
+   *   The item returned by \Drupal\Core\Queue\QueueInterface::claimItem().
+   *
+   * @see \Drupal\Core\Queue\QueueInterface::deleteItem()
+   */
+  public function deleteQueueItem($item);
+}