diff --git a/core/modules/system/tests/src/Unit/EventSubscriber/AdminRouteSubscriberTest.php b/core/modules/system/tests/src/Unit/EventSubscriber/AdminRouteSubscriberTest.php
new file mode 100644
index 0000000000..b938dd4684
--- /dev/null
+++ b/core/modules/system/tests/src/Unit/EventSubscriber/AdminRouteSubscriberTest.php
@@ -0,0 +1,93 @@
+<?php
+
+namespace Drupal\Tests\system\Unit\EventSubscriber;
+
+use Drupal\Core\Routing\RouteBuildEvent;
+use Drupal\system\EventSubscriber\AdminRouteSubscriber;
+use Drupal\Tests\UnitTestCase;
+use Symfony\Component\Routing\Route;
+use Symfony\Component\Routing\RouteCollection;
+
+/**
+ * @coversDefaultClass \Drupal\system\EventSubscriber\AdminRouteSubscriber
+ * @group system
+ */
+class AdminRouteSubscriberTest extends UnitTestCase {
+
+  /**
+   * @dataProvider providerTestAlterRoutes
+   */
+  public function testAlterRoutes(RouteCollection $expected_collection, RouteCollection $collection) {
+    $admin_route_subscriber = new AdminRouteSubscriber();
+    $admin_route_subscriber->onAlterRoutes(new RouteBuildEvent($collection));
+
+    $this->assertEquals($expected_collection, $collection);
+  }
+
+  public function providerTestAlterRoutes() {
+    $non_admin_route = new Route('/front-page');
+    $non_admin_route_html = new Route('/front-page', [], ['_format' => 'html']);
+    $non_admin_route_non_html = new Route('/front-page', [], ['_format' => 'json']);
+
+    $admin_route = new Route('/admin/test');
+    $admin_route_html = new Route('/admin/test', [], ['_format' => 'html']);
+    $admin_route_non_html = new Route('/admin/test', [], ['_format' => 'json']);
+
+    $expected_collection = new RouteCollection();
+    $expected_collection->add('route.name', clone $non_admin_route);
+    $collection = new RouteCollection();
+    $collection->add('route.name', clone $non_admin_route);
+    $data['non admin route'] = [
+      $expected_collection,
+      $collection,
+    ];
+
+    $expected_collection = new RouteCollection();
+    $expected_collection->add('route.name', clone $non_admin_route_html);
+    $collection = new RouteCollection();
+    $collection->add('route.name', clone $non_admin_route_html);
+    $data['non admin route with explicit html'] = [
+      $expected_collection,
+      $collection,
+    ];
+
+    $expected_collection = new RouteCollection();
+    $expected_collection->add('route.name', clone $non_admin_route_non_html);
+    $collection = new RouteCollection();
+    $collection->add('route.name', clone $non_admin_route_non_html);
+    $data['non admin route with explicit json'] = [
+      $expected_collection,
+      $collection,
+    ];
+
+    $expected_collection = new RouteCollection();
+    $expected_collection->add('route.name', (clone $admin_route)->setOption('_admin_route', TRUE));
+    $collection = new RouteCollection();
+    $collection->add('route.name', clone $admin_route);
+    $data['admin route'] = [
+      $expected_collection,
+      $collection,
+    ];
+
+    $expected_collection = new RouteCollection();
+    $expected_collection->add('route.name', (clone $admin_route_html)->setOption('_admin_route', TRUE));
+    $collection = new RouteCollection();
+    $collection->add('route.name', clone $admin_route_html);
+    $data['admin route with explicit html'] = [
+      $expected_collection,
+      $collection,
+    ];
+
+    $expected_collection = new RouteCollection();
+    $expected_collection->add('route.name', clone $admin_route_non_html);
+    $collection = new RouteCollection();
+    $collection->add('route.name', clone $admin_route_non_html);
+    $data['admin route with explicit json'] = [
+      $expected_collection,
+      $collection,
+    ];
+
+    return $data;
+  }
+
+}