diff -u b/core/modules/user/src/AccountForm.php b/core/modules/user/src/AccountForm.php
--- b/core/modules/user/src/AccountForm.php
+++ b/core/modules/user/src/AccountForm.php
@@ -16,6 +16,7 @@
 use Drupal\user\Plugin\LanguageNegotiation\LanguageNegotiationUser;
 use Drupal\user\Plugin\LanguageNegotiation\LanguageNegotiationUserAdmin;
 use Symfony\Component\DependencyInjection\ContainerInterface;
+use Drupal\Core\Database\Database;
 
 /**
  * Form controller for the user account forms.
@@ -448,6 +449,8 @@
     $account = $this->entity;
     $name = $form_state->getValue('name');
     $mail = $form_state->getValue('mail');
+    // Get a list of files in the database for this directory.
+    $database = Database::getConnection();
 
     // For new registrations, make sure the username does not conflict with
     // an existing user's email address.
@@ -457,8 +460,8 @@
       // For existing users whose username matches another user's email address
       // are not forced to update their username.
       if ($account->isAuthenticated()) {
-        $name_taken = (bool) db_select('users_field_data', 'ufd')
-          ->condition('ufd.name', db_like($name), 'LIKE')
+        $name_taken = (bool) $database->select('users_field_data', 'ufd')
+          ->condition('ufd.name', '%' . $database->escapeLike($search_phrase) . '%', 'LIKE')
           ->condition('ufd.uid', $account->id(), '<>')
           ->range(0, 1)
           ->countQuery()
@@ -466,11 +469,11 @@
           ->fetchField();
       }
       else {
-        $name_taken = (bool) db_select('users_field_data', 'ufd')
+        $name_taken = (bool) $database->select('users_field_data', 'ufd')
           ->condition(
                     db_or()
-                      ->condition('ufd.name', db_like($name), 'LIKE')
-                      ->condition('ufd.mail', db_like($name), 'LIKE')
+                      ->condition('ufd.name', '%' . $database->escapeLike($search_phrase) . '%', 'LIKE')
+                      ->condition('ufd.mail', '%' . $database->escapeLike($search_phrase) . '%', 'LIKE')
                 )
           ->condition('ufd.status', 1)
           ->range(0, 1)
@@ -492,8 +495,8 @@
       // For existing users whose email matches another user's username are not
       // forced to update their email address.
       if ($account->isAuthenticated()) {
-        $mail_taken = (bool) db_select('users_field_data', 'ufd')
-          ->condition('ufd.mail', db_like($mail), 'LIKE')
+        $mail_taken = (bool) $database->select('users_field_data', 'ufd')
+          ->condition('ufd.mail', '%' . $database->escapeLike($search_phrase) . '%', 'LIKE')
           ->condition('ufd.uid', $account->id(), '<>')
           ->range(0, 1)
           ->countQuery()
@@ -501,11 +504,11 @@
           ->fetchField();
       }
       else {
-        $mail_taken = (bool) db_select('users_field_data', 'ufd')
+        $mail_taken = (bool) $database->select('users_field_data', 'ufd')
           ->condition(
                     db_or()
-                      ->condition('ufd.mail', db_like($mail), 'LIKE')
-                      ->condition('ufd.name', db_like($mail), 'LIKE')
+                      ->condition('ufd.name', '%' . $database->escapeLike($search_phrase) . '%', 'LIKE')
+                      ->condition('ufd.mail', '%' . $database->escapeLike($search_phrase) . '%', 'LIKE')
                 )
           ->condition('ufd.status', 1)
           ->range(0, 1)
diff -u b/core/modules/user/src/Form/UserPasswordForm.php b/core/modules/user/src/Form/UserPasswordForm.php
--- b/core/modules/user/src/Form/UserPasswordForm.php
+++ b/core/modules/user/src/Form/UserPasswordForm.php
@@ -16,6 +16,8 @@
 use Drupal\Core\Site\Settings;
 use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Url;
+use Drupal\user\UserInterface;
+use Drupal\Core\Messenger\MessengerInterface;
 
 /**
  * Provides a user password reset form.
@@ -275,14 +277,14 @@
     }
     if (isset($account)) {
       // Mail one-time login URL and instructions using current language.
-      $mail = _user_mail_notify('password_reset', $account, $language_interface->getId());
+      $mail = _user_mail_notify('password_reset', $account);
       if (!empty($mail)) {
         $this->logger('user')->notice('Password reset instructions mailed to %name at %email.', [
           '
         %name' => $account->name,
           '%email' => $account->mail,
         ]);
-        \Drupal::messenger($this->t('Further instructions have been sent to your e-mail address.'));
+        \Drupal::messenger()->addMessage($this->t('Further instructions have been sent to your e-mail address.'));
       }
 
       $form_state->setRedirectUrl(Url::fromRoute('user.page'));
diff -u b/core/modules/user/tests/src/Functional/UserEditTest.php b/core/modules/user/tests/src/Functional/UserEditTest.php
--- b/core/modules/user/tests/src/Functional/UserEditTest.php
+++ b/core/modules/user/tests/src/Functional/UserEditTest.php
@@ -265,14 +265,14 @@
 
     // Test that the first user can save their account with no errors.
     $this->drupalLogin($user_with_email);
-    $this->drupalPostForm("user/" . $user_with_email->id() . "/edit", [], t('Save'));
-    $this->assertText(t("The changes have been saved."), "The user does not need to change their username if it matches another user's email address.");
+    $this->submitForm("user/" . $user_with_email->id() . "/edit", [], t('Save'));
+    $this->assertSession()->responseContains(t("The changes have been saved."), "The user does not need to change their username if it matches another user's email address.");
     $this->drupalLogout();
 
     // Test that the second user can save their account with no errors.
     $this->drupalLogin($user_with_name);
-    $this->drupalPostForm("user/" . $user_with_name->id() . "/edit", [], t('Save'));
-    $this->assertText(t("The changes have been saved."), "The user does not need to change their email address if it matches another user's username.");
+    $this->submitForm("user/" . $user_with_name->id() . "/edit", [], t('Save'));
+    $this->assertSession()->responseContains(t("The changes have been saved."), "The user does not need to change their email address if it matches another user's username.");
   }
 
 }
diff -u b/core/modules/user/tests/src/Functional/UserPasswordResetTest.php b/core/modules/user/tests/src/Functional/UserPasswordResetTest.php
--- b/core/modules/user/tests/src/Functional/UserPasswordResetTest.php
+++ b/core/modules/user/tests/src/Functional/UserPasswordResetTest.php
@@ -250,7 +250,7 @@
     $user_settings->set('verify_mail', FALSE)->save();
 
     // Don't require admin approval for new accounts.
-    $user_settings->set('register', USER_REGISTER_VISITORS)->save();
+    $user_settings->set('register', REGISTER_VISITORS)->save();
     // Create two users.
     $user_with_email = $this->drupalCreateUser();
     $user_with_name = $this->drupalCreateUser();
@@ -263,26 +263,26 @@
     // Try and reset based on the duplicated email.
     $edit = [];
     $edit['name'] = $user_with_email->getEmail();
-    $this->drupalPostForm('user/password', $edit, t('Submit'));
+    $this->submitForm('user/password', $edit, t('Submit'));
     // There should be a field prompting the user to pick and account.
-    $this->assertField('choose_account', 'User is prompted to pick an account when email matches two accounts.');
+    $this->assertSession()->fieldExists('choose_account', 'User is prompted to pick an account when email matches two accounts.');
     // We should be sure to not expose another user's email to the user.
-    $this->assertNoText($user_with_name->getEmail(), "Duplicated user's email is not exposed to the other user.");
+    $this->assertSession()->pageTextNotContains($user_with_name->getEmail(), "Duplicated user's email is not exposed to the other user.");
 
     // Select the account with the username matching the entered email.
     $edit = [];
     $edit['choose_account'] = Crypt::hashBase64(Settings::getHashSalt() . $user_with_email->id());
-    $this->drupalPostForm(NULL, $edit, t('Submit'));
-    $this->assertText(t('Further instructions have been sent to your e-mail address.'), 'User is notified that password reset was sent.');
+    $this->submitForm(NULL, $edit, t('Submit'));
+    $this->assertSession()->pageTextContains(t('Further instructions have been sent to your e-mail address.'), 'User is notified that password reset was sent.');
 
     // Make sure that right user was sent a reset email.
-    $this->assertEqual(count($this->drupalGetMails([
+    $this->assertEquals(count($this->drupalGetMails([
       'key' => 'password_reset',
       'to' => $user_with_email->getEmail(),
     ]
     )), 1, 'The right user was sent a password reset mail.');
     // Make sure that the other user was not sent an email.
-    $this->assertEqual(count($this->drupalGetMails([
+    $this->assertEquals(count($this->drupalGetMails([
       'key' => 'password_reset',
       'to' => $user_with_name->getEmail(),
     ])), 0, 'The other user was not sent a password reset mail.');
@@ -292,11 +292,11 @@
     $this->drupalLogin($user_with_name);
     $this->drupalGet('user/password');
     // There should not be a form element for name.
-    $this->assertNoField('name', 'Duplicate user is not asked for a name when resetting password while logged in.');
-    $this->drupalPostForm(NULL, [], t('Submit'));
+    $this->assertSession()->fieldNotExists('name', 'Duplicate user is not asked for a name when resetting password while logged in.');
+    $this->submitForm(NULL, [], t('Submit'));
     // Make sure the user with the matching username was sent an email.
-    $this->assertText(t('Further instructions have been sent to your e-mail address.'), 'User is notified that password reset was sent when logged in.');
-    $this->assertEqual(count($this->drupalGetMails(
+    $this->assertSession()->pageTextContains(t('Further instructions have been sent to your e-mail address.'), 'User is notified that password reset was sent when logged in.');
+    $this->assertEquals(count($this->drupalGetMails(
       [
         'key' => 'password_reset',
         'to' => $user_with_name->getEmail(),
@@ -304,7 +304,7 @@
     // Make sure that the user with the matching
     // email address was not sent an email.
     // (An email was already sent to this user earlier.)
-    $this->assertEqual(count($this->drupalGetMails(
+    $this->assertEquals(count($this->drupalGetMails(
       [
         'key' => 'password_reset',
         'to' => $user_with_email->getEmail(),
diff -u b/core/modules/user/tests/src/Functional/UserRegistrationTest.php b/core/modules/user/tests/src/Functional/UserRegistrationTest.php
--- b/core/modules/user/tests/src/Functional/UserRegistrationTest.php
+++ b/core/modules/user/tests/src/Functional/UserRegistrationTest.php
@@ -29,7 +29,9 @@
   protected $defaultTheme = 'stark';
 
   /**
+   * Tests registration of user with email verification.
    *
+   * @group user
    */
   public function testRegistrationWithEmailVerification() {
     $config = $this->config('user.settings');
@@ -74,7 +76,9 @@
   }
 
   /**
+   * Tests registration of user without email verification.
    *
+   * @group user
    */
   public function testRegistrationWithoutEmailVerification() {
     $config = $this->config('user.settings');
@@ -149,7 +153,9 @@
   }
 
   /**
+   * Tests registration of user with email duplicates.
    *
+   * @group user
    */
   public function testRegistrationEmailDuplicates() {
     // Don't require email verification and allow registration by site visitors
@@ -250,7 +256,9 @@
   }
 
   /**
+   * Tests registration of user with default values.
    *
+   * @group user
    */
   public function testRegistrationDefaultValues() {
     // Don't require email verification and allow registration by site visitors
@@ -432,7 +440,7 @@
     $user_settings->set('verify_mail', FALSE)->save();
 
     // Don't require admin approval for new accounts.
-    $user_settings->set('register', USER_REGISTER_VISITORS)->save();
+    $user_settings->set('register', REGISTER_VISITORS)->save();
 
     // Set up a user to check for duplicates.
     $duplicate_user = $this->drupalCreateUser();
@@ -445,8 +453,8 @@
 
     // Attempt to create a new account using a username that matches an
     // existing email.
-    $this->drupalPostForm('user/register', $edit, t('Create new account'));
-    $this->assertText(t('The name @name is already taken.', ['@name' => $edit['name']]), "A user cannot be created when their username matches an existing user's email address.");
+    $this->submitForm('user/register', $edit, t('Create new account'));
+    $this->assertSession()->pageTextContains(t('The name @name is already taken.', ['@name' => $edit['name']]), "A user cannot be created when their username matches an existing user's email address.");
 
     // Change the username to an email address.
     $duplicate_user->name = $name = $this->randomMachineName() . '@example.com';
@@ -458,8 +466,8 @@
 
     // Attempt to create a new account using an email that matches an existing
     // username.
-    $this->drupalPostForm('user/register', $edit, t('Create new account'));
-    $this->assertText(t('The email address @email is already registered.', ['@email' => $edit['mail']]), "A user cannot be created when their email address matches an existing username.");
+    $this->submitForm('user/register', $edit, t('Create new account'));
+    $this->assertSession()->pageTextContains(t('The email address @email is already registered.', ['@email' => $edit['mail']]), "A user cannot be created when their email address matches an existing username.");
   }
 
 }
reverted:
--- b/core/modules/user/user.module
+++ a/core/modules/user/user.module
@@ -29,8 +29,6 @@
 use Drupal\user\Entity\User;
 use Drupal\user\RoleInterface;
 use Drupal\user\UserInterface;
-use Drupal\Core\Language\LanguageInterface;
-use Symfony\Component\HttpKernel\HttpKernelInterface;
 
 /**
  * Implements hook_help().