diff --git a/core/tests/Drupal/Nightwatch/Commands/drupalCreateRole.js b/core/tests/Drupal/Nightwatch/Commands/drupalCreateRole.js
index ed6917b9cb..aa9aa20bfe 100644
--- a/core/tests/Drupal/Nightwatch/Commands/drupalCreateRole.js
+++ b/core/tests/Drupal/Nightwatch/Commands/drupalCreateRole.js
@@ -22,6 +22,8 @@ exports.command = function drupalCreateRole({ permissions, name = null }, callba
       this
         .drupalRelativeURL('/admin/people/roles/add')
         .setValue('input[name="label"]', roleName)
+        /* Wait for the machine name to appear so that it can be used later to
+         select the permissions from the permission page. */
         .expect.element('.user-role-form .machine-name-value').to.be.visible.before(2000);
 
       this.perform((done) => {
diff --git a/core/tests/Drupal/Nightwatch/Commands/drupalLogin.js b/core/tests/Drupal/Nightwatch/Commands/drupalLogin.js
index d957fc7808..fb36ae0c11 100644
--- a/core/tests/Drupal/Nightwatch/Commands/drupalLogin.js
+++ b/core/tests/Drupal/Nightwatch/Commands/drupalLogin.js
@@ -25,4 +25,4 @@ exports.command = function drupalLogin({ name, password }) {
   });
 
   return this;
-};
\ No newline at end of file
+};
diff --git a/core/tests/Drupal/Nightwatch/Commands/drupalUserIsLoggedIn.js b/core/tests/Drupal/Nightwatch/Commands/drupalUserIsLoggedIn.js
index a05e4b686b..d788b15cc4 100644
--- a/core/tests/Drupal/Nightwatch/Commands/drupalUserIsLoggedIn.js
+++ b/core/tests/Drupal/Nightwatch/Commands/drupalUserIsLoggedIn.js
@@ -16,4 +16,4 @@ exports.command = function drupalUserIsLoggedIn(callback) {
   }
 
   return this;
-};
\ No newline at end of file
+};
diff --git a/core/tests/Drupal/TestSite/Commands/TestSiteUserLoginCommand.php b/core/tests/Drupal/TestSite/Commands/TestSiteUserLoginCommand.php
index c178e5653b..c990f9bc12 100644
--- a/core/tests/Drupal/TestSite/Commands/TestSiteUserLoginCommand.php
+++ b/core/tests/Drupal/TestSite/Commands/TestSiteUserLoginCommand.php
@@ -2,14 +2,10 @@
 
 namespace Drupal\TestSite\Commands;
 
-use Drupal\Core\Database\Database;
 use Drupal\Core\DrupalKernel;
 use Drupal\Core\Site\Settings;
-use Drupal\Core\Test\FunctionalTestSetupTrait;
-use Drupal\Core\Test\TestDatabase;
-use Drupal\Core\Test\TestRunnerKernel;
-use Drupal\Core\Test\TestSetupTrait;
 use Symfony\Component\Console\Command\Command;
+use Symfony\Component\Console\Exception\InvalidArgumentException;
 use Symfony\Component\Console\Input\InputArgument;
 use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Input\InputOption;
@@ -17,7 +13,7 @@
 use Symfony\Component\HttpFoundation\Request;
 
 /**
- * Command to get a login link for the test site.
+ * Command to generate a login link for the test site.
  *
  * @internal
  */
@@ -51,13 +47,15 @@ class TestSiteUserLoginCommand extends Command {
    */
   protected function configure() {
     $this->setName('user-login')
-      ->setDescription('Display a one time login link for an user.')
+      ->setDescription('Generate a one time login link for an user.')
       ->addArgument('uid', InputArgument::OPTIONAL, 'The id of the user to which the link will be generated', 1)
       ->addOption('site-path', NULL, InputOption::VALUE_REQUIRED, 'The path for the test site.');
   }
 
   /**
    * {@inheritdoc}
+   *
+   * @throws \Symfony\Component\Console\Exception\InvalidArgumentException
    */
   protected function execute(InputInterface $input, OutputInterface $output) {
     $root = dirname(dirname(dirname(dirname(dirname(__DIR__)))));
@@ -75,10 +73,13 @@ protected function execute(InputInterface $input, OutputInterface $output) {
     $kernel->boot();
 
     $container = $kernel->getContainer();
-
+    $uid = $input->getArgument('uid');
+    if (!is_numeric($uid)) {
+      throw new InvalidArgumentException(sprintf('The "%s" argument does not exist.', $name));
+    }
     $userEntity = $container->get('entity_type.manager')
       ->getStorage('user')
-      ->load($input->getArgument('uid'));
+      ->load($uid);
     $url = user_pass_reset_url($userEntity) . '/login';
     $output->writeln($url);
   }