Installed twig with composer require twig command.

config/bundles.php

@@ -2,4 +2,6 @@
 
 return [
     Symfony\Bundle\FrameworkBundle\FrameworkBundle::class => ['all' => true],
+    Symfony\Bundle\TwigBundle\TwigBundle::class => ['all' => true],
+    Twig\Extra\TwigExtraBundle\TwigExtraBundle::class => ['all' => true],
 ];

config/packages/twig.yaml

@@ -0,0 +1,6 @@
+twig:
+    file_name_pattern: '*.twig'
+
+when@test:
+    twig:
+        strict_variables: true