fix(symfony): upgrade command requires phpunit (#4968)

fixes #4950

Author: soyuka

src/Core/Bridge/Symfony/Bundle/Command/UpgradeApiResourceCommand.php

@@ -89,6 +89,12 @@ protected function execute(InputInterface $input, OutputInterface $output): int
             return Command::INVALID;
         }
 
+        if (!class_exists(NodeTraverser::class)) {
+            $output->writeln('Run `composer require --dev `nikic/php-parser` or install phpunit to use this command.');
+
+            return Command::FAILURE;
+        }
+
         $subresources = $this->getSubresources();
 
         $prettyPrinter = new Standard();
@@ -142,6 +148,12 @@ protected function execute(InputInterface $input, OutputInterface $output): int
                     continue;
                 }
 
+                if (!class_exists(Differ::class)) {
+                    $output->writeln('Run `composer require --dev sebastian/diff` or install phpunit to print a diff.');
+
+                    return Command::FAILURE;
+                }
+
                 $this->printDiff($oldCode, $newCode, $output);
                 continue;
             }