Make the mock FinalMatcher a real matcher, since it's useful on its own.

core/lib/Drupal/Core/Routing/FinalMatcherInterface.php

@@ -10,6 +10,15 @@
  */
 interface FinalMatcherInterface {
 
+  /**
+   * Sets the route collection this matcher should use.
+   *
+   * @param RouteCollection $collection
+   *   The collection against which to match.
+   *
+   * @return FinalMatcherInterface
+   *   The current matcher.
+   */
   public function setCollection(RouteCollection $collection);
 
   /**

core/modules/system/lib/Drupal/system/Tests/Routing/MockFinalMatcher.php → core/lib/Drupal/Core/Routing/FirstEntryFinalMatcher.php

 <?php
 
-namespace Drupal\system\Tests\Routing;
+namespace Drupal\Core\Routing;
 
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\Routing\Route;
 use Symfony\Component\Routing\RouteCollection;
 
-use Drupal\Core\Routing\FinalMatcherInterface;
-
-
 /**
- * Mock final matcher for testing.
+ * Final matcher that simply returns the first item in the remaining routes.
  *
  * This class simply matches the first remaining route.
  */
-class MockFinalMatcher implements FinalMatcherInterface {
+class FirstEntryFinalMatcher implements FinalMatcherInterface {
+
+  /**
+   * The RouteCollection this matcher should match against.
+   *
+   * @var RouteCollection
+   */
   protected $routes;
 
+  /**
+   * Sets the route collection this matcher should use.
+   *
+   * @param RouteCollection $collection
+   *   The collection against which to match.
+   *
+   * @return FinalMatcherInterface
+   *   The current matcher.
+   */
   public function setCollection(RouteCollection $collection) {
     $this->routes = $collection;
 
@@ -25,7 +37,7 @@ public function setCollection(RouteCollection $collection) {
 
 
   public function matchRequest(Request $request) {
-    // For testing purposes, just return whatever the first route is.
+    // Return whatever the first route in the collection is.
     foreach ($this->routes as $name => $route) {
       return array_merge($this->mergeDefaults(array(), $route->getDefaults()), array('_route' => $name));
     }

core/modules/system/lib/Drupal/system/Tests/Routing/HttpMethodMatcherTest.php

@@ -15,6 +15,7 @@
 use Drupal\simpletest\UnitTestBase;
 use Drupal\Core\Routing\HttpMethodMatcher;
 use Drupal\Core\Routing\NestedMatcher;
+use Drupal\Core\Routing\FirstEntryFinalMatcher;
 
 use Exception;
 
@@ -74,7 +75,7 @@ public function testNestedMatcher() {
 
     $matcher->setInitialMatcher(new MockPathMatcher($this->fixtures->sampleRouteCollection()));
     $matcher->addPartialMatcher(new HttpMethodMatcher());
-    $matcher->setFinalMatcher(new MockFinalMatcher());
+    $matcher->setFinalMatcher(new FirstEntryFinalMatcher());
 
     $request = Request::create('/path/one', 'GET');