diff -u b/core/modules/user/tests/src/Functional/UserLoginTest.php b/core/modules/user/tests/src/Functional/UserLoginTest.php
--- b/core/modules/user/tests/src/Functional/UserLoginTest.php
+++ b/core/modules/user/tests/src/Functional/UserLoginTest.php
@@ -5,6 +5,7 @@
 use Drupal\Core\Url;
 use Drupal\Tests\BrowserTestBase;
 use Drupal\user\Entity\User;
+use Drupal\user\UserInterface;
 
 /**
  * Ensure that login works as expected.
@@ -120,10 +121,10 @@
    * Tests user password is re-hashed upon login after changing $count_log2.
    */
   public function testPasswordRehashOnLogin() {
-    // Determine default log2 for phpass hashing algorithm
+    // Determine default log2 for phpass hashing algorithm.
     $default_count_log2 = 16;
 
-    // Retrieve instance of password hashing algorithm
+    // Retrieve instance of password hashing algorithm.
     $password_hasher = $this->container->get('password');
 
     // Create a new user and authenticate.
@@ -176,8 +177,18 @@
 
   /**
    * Helper to test log in with a maximum length password.
+   *
+   * @param \Drupal\user\UserInterface $account
+   *   An object containing the user account.
+   * @param string $current_password
+   *   The current password associated with the user.
+   * @param int $length
+   *   The length of the password.
+   *
+   * @return string
+   *   The new password associated with the user.
    */
-  public function doPasswordLengthLogin($account, $current_password, $length) {
+  public function doPasswordLengthLogin(UserInterface $account, string $current_password, int $length) {
     $new_password = \Drupal::service('password_generator')->generate($length);
     $uid = $account->id();
     $edit = [
@@ -189,16 +200,17 @@
 
     // Change the password.
     $this->drupalGet("user/$uid/edit");
-    $this->drupalPostForm(NULL, $edit, 'Save');
-    $this->assertSession()->responseContains('The changes have been saved.');
+    $this->submitForm($edit, 'Save');
+    $this->assertSession()->pageTextContains('The changes have been saved.');
     $this->drupalLogout();
 
     // Login with new password.
+    $this->drupalGet('user/login');
     $edit = [
       'name' => $account->getAccountName(),
       'pass' => $new_password,
     ];
-    $this->drupalPostForm('user/login', $edit, 'Log in');
+    $this->submitForm($edit, 'Log in');
     return $new_password;
   }