diff --git a/core/modules/user/tests/src/FunctionalJavascript/RegistrationWithUserFieldsTest.php b/core/modules/user/tests/src/FunctionalJavascript/RegistrationWithUserFieldsTest.php
new file mode 100644
index 0000000000..f013b7a3bf
--- /dev/null
+++ b/core/modules/user/tests/src/FunctionalJavascript/RegistrationWithUserFieldsTest.php
@@ -0,0 +1,176 @@
+<?php
+
+namespace Drupal\Tests\user\FunctionalJavascript;
+
+use Drupal\FunctionalJavascriptTests\JavascriptTestBase;
+use Drupal\Core\Field\FieldStorageDefinitionInterface;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\Core\Entity\Entity\EntityFormDisplay;
+
+/**
+ * Tests user registration forms with additional fields.
+ *
+ * @group user
+ */
+class RegistrationWithUserFieldsTest extends JavascriptTestBase {
+
+  /**
+   * @var \Drupal\FunctionalJavascriptTests\JSWebAssert;
+   */
+  private $webAssert;
+
+  /**
+   * @var \Behat\Mink\Element\DocumentElement;
+   */
+  private $page;
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = ['field_test'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+    $this->page = $this->getSession()->getPage();
+    $this->webAssert = $this->assertSession();
+  }
+
+  /**
+   * Tests Field API fields on user registration forms.
+   */
+  public function testRegistrationWithUserFields() {
+    // Create a field on 'user' entity type.
+    $field_storage = FieldStorageConfig::create([
+      'field_name' => 'test_user_field',
+      'entity_type' => 'user',
+      'type' => 'test_field',
+      'cardinality' => 1,
+    ]);
+    $field_storage->save();
+    $field = FieldConfig::create([
+      'field_storage' => $field_storage,
+      'label' => 'Some user field',
+      'bundle' => 'user',
+      'required' => TRUE,
+    ]);
+    $field->save();
+
+    entity_get_form_display('user', 'user', 'default')
+      ->setComponent('test_user_field', ['type' => 'test_field_widget'])
+      ->save();
+    entity_get_form_display('user', 'user', 'register')
+      ->save();
+
+//    EntityFormDisplay::load('user.user.default')
+//      ->setComponent('test_user_field', ['type' => 'test_field_widget'])
+//      ->save();
+//    EntityFormDisplay::load('user.user.register')
+//      ->save();
+
+    // Check that the field does not appear on the registration form.
+    $this->drupalGet('user/register');
+    $this->webAssert->pageTextNotContains($field->label());
+    $this->webAssert->responseHeaderContains('X-Drupal-Cache-Tags','config:core.entity_form_display.user.user.register');
+    $this->webAssert->responseHeaderContains('X-Drupal-Cache-Tags','config:user.settings');
+
+//    // Have the field appear on the registration form.
+//    EntityFormDisplay::load('user.user.register')
+//      ->setComponent('test_user_field', ['type' => 'test_field_widget'])
+//      ->save();
+
+    // Have the field appear on the registration form.
+    entity_get_form_display('user', 'user', 'register')
+      ->setComponent('test_user_field', ['type' => 'test_field_widget'])
+      ->save();
+
+    $this->drupalGet('user/register');
+    $this->webAssert->pageTextContains($field->label());
+    $this->assertRegistrationFormCacheTagsWithUserFields();
+
+    // Check that validation errors are correctly reported.
+    $name = $this->webAssert->waitForField('edit-name');
+    $name->setValue($this->randomMachineName());
+
+    $mail = $this->webAssert->waitForField('edit-mail');
+    $mail->setValue($name->getValue() . '@example.com');
+
+    $this->page->findButton('edit-submit')->click();
+    $this->webAssert->assertWaitOnAjaxRequest();
+    $this->assertRegistrationFormCacheTagsWithUserFields();
+    $this->webAssert->pageTextContains(t('@name field is required.', ['@name' => $field->label()]));
+
+    // Invalid input.
+    $test_user_field = $this->webAssert->waitForField('test_user_field[0][value]');
+    $test_user_field->setValue('-1');
+    $this->page->findButton('edit-submit')->click();
+    $this->webAssert->assertWaitOnAjaxRequest();
+    $this->assertRegistrationFormCacheTagsWithUserFields();
+    $this->webAssert->pageTextContains(t('%name does not accept the value -1.', ['%name' => $field->label()]));
+
+    // Submit with valid data.
+    $value = mt_rand(1, 255);
+    $test_user_field->setValue($value);
+    $this->page->findButton('edit-submit')->click();
+
+    // Check user fields.
+    $accounts = $this->container->get('entity_type.manager')->getStorage('user')
+      ->loadByProperties(['name' => $name, 'mail' => $mail]);
+    $new_user = reset($accounts);
+    $this->assertEquals($value, $new_user->test_user_field->value,'The field value was correctly saved.');
+
+    // Check that the 'add more' button works.
+    $field_storage->setCardinality(FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED);
+    $field_storage->save();
+    foreach (['js', 'nojs'] as $js) {
+      $this->drupalGet('user/register');
+      $this->assertRegistrationFormCacheTagsWithUserFields();
+      // Add two inputs.
+      $value = mt_rand(1, 255);
+      $test_user_field->setValue($value);
+      if ($js == 'js') {
+        $field_test_user_add_more = $this->page->find('css', 'input[name="test_user_field_add_more"]');
+        $field_test_user_add_more->click();
+        $field_test_user_add_more->click();
+      }
+      else {
+        $this->page->findButton(t('Add another item'))->click();
+        $this->page->findButton(t('Add another item'))->click();
+      }
+      // Submit with three values.
+      $first_test_user_field = $this->webAssert->waitForField('test_user_field[1][value]');
+      $first_test_user_field->setValue($value + 1);
+      $second_test_user_field = $this->webAssert->waitForField('test_user_field[2][value]');
+      $second_test_user_field->setValue($value + 2);
+
+      $name = $this->webAssert->waitForField('name');
+      $name->setValue($this->randomMachineName());
+      $mail = $this->webAssert->waitForField('email');
+      $mail->setValue($name->getValue() . '@example.com');
+      $this->page->findButton('edit-submit')->click();
+      // Check user fields.
+      $accounts = $this->container->get('entity_type.manager')->getStorage('user')
+        ->loadByProperties(['name' => $name, 'mail' => $mail]);
+      $new_user = reset($accounts);
+      $this->assertEquals($value, $new_user->test_user_field[0]->value, t('@js : The field value was correctly saved.', ['@js' => $js]));
+      $this->assertEquals($value + 1, $new_user->test_user_field[1]->value, t('@js : The field value was correctly saved.', ['@js' => $js]));
+      $this->assertEquals($value + 2, $new_user->test_user_field[2]->value, t('@js : The field value was correctly saved.', ['@js' => $js]));
+    }
+  }
+
+  /**
+   * Asserts the presence of cache tags on registration form with user fields.
+   */
+  protected function assertRegistrationFormCacheTagsWithUserFields() {
+    $this->webAssert->responseHeaderContains('X-Drupal-Cache-Tags','config:core.entity_form_display.user.user.register');
+    $this->webAssert->responseHeaderContains('X-Drupal-Cache-Tags','config:field.field.user.user.test_user_field');
+    $this->webAssert->responseHeaderContains('X-Drupal-Cache-Tags','config:field.storage.user.test_user_field');
+    $this->webAssert->responseHeaderContains('X-Drupal-Cache-Tags','config:user.settings');
+  }
+
+}
diff --git a/core/modules/user/tests/src/Kernel/WhosOnlineBlockTest.php b/core/modules/user/tests/src/Kernel/WhosOnlineBlockTest.php
new file mode 100644
index 0000000000..248e670d17
--- /dev/null
+++ b/core/modules/user/tests/src/Kernel/WhosOnlineBlockTest.php
@@ -0,0 +1,89 @@
+<?php
+
+namespace Drupal\Tests\user\Kernel;
+
+use Drupal\block\Entity\Block;
+use Drupal\KernelTests\KernelTestBase;
+use Drupal\user\Entity\User;
+
+/**
+ * Tests the Who's Online Block.
+ *
+ * @group user
+ */
+class WhosOnlineBlockTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['system', 'user', 'block', 'views'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+    $this->installConfig(['system', 'block', 'views', 'user']);
+    $this->installSchema('system', ['sequences']);
+    $this->installEntitySchema('user');
+
+  }
+
+  /**
+   * Test the Who's Online block.
+   */
+  public function testWhosOnlineBlock() {
+
+    // Generate users.
+    $user1 = User::create([
+      'name' => 'user1',
+      'mail' => 'user1@example.com',
+    ]);
+    $user1->addRole('administrator');
+    $user1->activate();
+    $user1->setLastAccessTime(\Drupal::time()->getRequestTime());
+    $user1->save();
+
+    $user2 = User::create([
+      'name' => 'user2',
+      'mail' => 'user2@example.com',
+    ]);
+    $user2->activate();
+    $user2->setLastAccessTime(\Drupal::time()->getRequestTime() + 1);
+    $user2->save();
+
+    $user3 = User::create([
+      'name' => 'user3',
+      'mail' => 'user2@example.com',
+    ]);
+    $user3->activate();
+    // Insert an inactive user who should not be seen in the block.
+    $inactive_time = \Drupal::time()->getRequestTime() - (15 * 60) - 1;
+    $user3->setLastAccessTime($inactive_time);
+    $user3->save();
+
+    // Test block output.
+    \Drupal::currentUser()->setAccount($user1);
+    // Create a block with only required values.
+    $block = Block::create([
+      'plugin' => 'views_block:who_s_online-who_s_online_block',
+      'region' => 'sidebar_first',
+      'id' => 'views_block__who_s_online_who_s_online_block',
+      'theme' => \Drupal::configFactory()->get('system.theme')->get('default'),
+      'label' => "Who's online",
+      'visibility' => [],
+      'weight' => 0,
+    ]);
+    $block->save();
+    $this->container->get('cache.render')->deleteAll();
+    $render_controller = \Drupal::entityTypeManager()->getViewBuilder($block->getEntityTypeId());
+    $content = $render_controller->view($block, 'block');
+    $this->setRawContent($this->render($content));
+    $this->assertRaw('2 users', 'Correct number of online users (2 users).');
+    $this->assertText($user1->getUsername(), 'Active user 1 found in online list.');
+    $this->assertText($user2->getUsername(), 'Active user 2 found in online list.');
+    $this->assertNoText($user3->getUsername(), 'Inactive user not found in online list.');
+    $this->assertTrue(strpos($this->getRawContent(), $user1->getUsername()) > strpos($this->getRawContent(), $user2->getUsername()), 'Online users are ordered correctly.');
+  }
+
+}