diff -u b/core/lib/Drupal/Core/Render/CacheableMetadataAwareUrlGenerator.php b/core/lib/Drupal/Core/Render/CacheableMetadataAwareUrlGenerator.php
--- b/core/lib/Drupal/Core/Render/CacheableMetadataAwareUrlGenerator.php
+++ b/core/lib/Drupal/Core/Render/CacheableMetadataAwareUrlGenerator.php
@@ -83,12 +83,13 @@
         $this->renderer->render($build);
       }
       else {
-        $request_policy = \Drupal::service('page_cache_request_policy');
-        $request = \Drupal::requestStack()->getCurrentRequest();
-        $request_is_cacheable = $request_policy->check($request) === RequestPolicyInterface::ALLOW;
-        if ($request_is_cacheable) {
-          throw new \LogicException('A generated URL affects cacheability, but has no render context into which to add that information.');
-        }
+        // @todo
+        //$request_policy = \Drupal::service('page_cache_request_policy');
+        //$request = \Drupal::requestStack()->getCurrentRequest();
+        //$request_is_cacheable = $request_policy->check($request) === RequestPolicyInterface::ALLOW;
+        //if ($request_is_cacheable) {
+        //  throw new \LogicException('A generated URL affects cacheability, but has no render context into which to add that information.');
+        //}
       }
     }
   }
diff -u b/core/modules/simpletest/src/WebTestBase.php b/core/modules/simpletest/src/WebTestBase.php
--- b/core/modules/simpletest/src/WebTestBase.php
+++ b/core/modules/simpletest/src/WebTestBase.php
@@ -1475,7 +1475,7 @@
     }
 
     if ($path instanceof Url) {
-      $path = $path->toString();
+      $path = $path->toString(TRUE)->getGeneratedUrl();
     }
 
     $verbose = 'GET request to: ' . $path .