diff -ru src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/TwigExtensionTest.php src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/TwigExtensionTest.php
--- src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/TwigExtensionTest.php	2020-06-01 21:10:48.134946072 +0000
+++ src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/TwigExtensionTest.php	2020-06-01 21:10:49.262921183 +0000
@@ -344,7 +344,7 @@
                 $loader = new YamlFileLoader($container, $locator);
                 break;
             default:
-                throw new \InvalidArgumentException(sprintf('Unsupported format: %s', $format));
+                throw new \InvalidArgumentException(sprintf('Unsupported format: "%s"', $format));
         }
 
         $loader->load($file.'.'.$format);