diff --git a/core/modules/update/tests/src/Unit/UpdateMailTest.php b/core/modules/update/tests/src/Unit/UpdateMailTest.php
new file mode 100644
index 0000000000000000000000000000000000000000..34f17d69c2e791c53fb4bea0c808a449fb926dfd
--- /dev/null
+++ b/core/modules/update/tests/src/Unit/UpdateMailTest.php
@@ -0,0 +1,230 @@
+<?php
+
+namespace Drupal\Tests\update\Unit;
+
+use Drupal\Core\DependencyInjection\ContainerBuilder;
+use Drupal\Tests\UnitTestCase;
+use Drupal\update\UpdateManagerInterface;
+
+/**
+ * Tests text of update email.
+ *
+ * @covers \update_mail
+ *
+ * @group update
+ */
+class UpdateMailTest extends UnitTestCase {
+
+ /**
+ * The container.
+ *
+ * @var \Drupal\Core\DependencyInjection\ContainerBuilder
+ */
+ protected $container;
+
+ /**
+ * The mocked current user service.
+ *
+ * @var \Drupal\Core\Session\AccountProxy|\PHPUnit\Framework\MockObject\MockObject
+ */
+ protected $currentUser;
+
+ /**
+ * Mocked language manager.
+ *
+ * @var \Drupal\language\ConfigurableLanguageManagerInterface|\PHPUnit\Framework\MockObject\MockObject
+ */
+ protected $languageManager;
+
+ /**
+ * Mocked config factory.
+ *
+ * @var \Drupal\Core\Config\ConfigFactory|\PHPUnit\Framework\MockObject\MockObject
+ */
+ protected $configFactory;
+
+ /**
+ * Mocked URL generator.
+ *
+ * @var \Drupal\Core\Render\MetadataBubblingUrlGenerator|\PHPUnit\Framework\MockObject\MockObject
+ */
+ protected $urlGenerator;
+
+ /**
+ * {@inheritdoc}
+ */
+ protected function setUp(): void {
+ parent::setUp();
+ include_once __DIR__ . '/../../../update.module';
+
+ // Initialize the container.
+ $this->container = new ContainerBuilder();
+ $this->container->set('string_translation', $this->getStringTranslationStub());
+ \Drupal::setContainer($this->container);
+
+ // Get needed mocks.
+ $this->currentUser = $this->createMock('\Drupal\Core\Session\AccountProxy');
+ $this->languageManager = $this->createMock('Drupal\language\ConfigurableLanguageManagerInterface');
+ $this->configFactory = $this->createMock('Drupal\Core\Config\ConfigFactory');
+ $this->urlGenerator = $this->createMock('\Drupal\Core\Render\MetadataBubblingUrlGenerator');
+ }
+
+ /**
+ * Test the subject and body of update text.
+ *
+ * @dataProvider providerTestUpdateEmail
+ */
+ public function testUpdateEmail($notification_threshold, $params, $authorized, array $expected_body) {
+ $langcode = 'en';
+ $available_updates_url = 'https://example.com/admin/reports/updates';
+ $update_settings_url = 'https://example.com/admin/reports/updates/settings';
+ $site_name = 'Test site';
+
+ // Initialize update_mail input parameters.
+ $key = NULL;
+ $message = [
+ 'langcode' => $langcode,
+ 'subject' => '',
+ 'message' => '',
+ 'body' => [],
+ ];
+
+ // Language manager just returns the language.
+ $this->languageManager
+ ->expects($this->once())
+ ->method('getLanguage')
+ ->willReturn($langcode);
+
+ // Create three config entities.
+ $config_site_name = $this->createMock('Drupal\Core\Config\Config');
+ $config_site_name
+ ->expects($this->once())
+ ->method('get')
+ ->with('name')
+ ->willReturn($site_name);
+ $config_notification = $this->createMock('Drupal\Core\Config\Config');
+ $config_notification
+ ->expects($this->once())
+ ->method('get')
+ ->with('notification.threshold')
+ ->willReturn($notification_threshold);
+
+ $this->configFactory
+ ->expects($this->exactly(2))
+ ->method('get')
+ ->will($this->returnValueMap([
+ ['system.site', $config_site_name],
+ ['update.settings', $config_notification],
+ ]));
+
+ // The calls to generateFromRoute differ if authorized.
+ $count = 2;
+ if ($authorized) {
+ $this->currentUser
+ ->expects($this->once())
+ ->method('hasPermission')
+ ->with('administer software updates')
+ ->willReturn(TRUE);
+ $count = 3;
+ }
+ // When authorized also get the URL for the route 'update.report_update'.
+ $this->urlGenerator
+ ->expects($this->exactly($count))
+ ->method('generateFromRoute')
+ ->will($this->returnValueMap([
+ ['update.status', [], ['absolute' => TRUE, 'language' => $langcode], FALSE, $update_settings_url],
+ ['update.settings', [], ['absolute' => TRUE], FALSE, $available_updates_url],
+ ['update.report_update', [], ['absolute' => TRUE, 'language' => $langcode], FALSE, $available_updates_url],
+ ]));
+
+ // Set the container.
+ $this->container->set('language_manager', $this->languageManager);
+ $this->container->set('url_generator', $this->urlGenerator);
+ $this->container->set('config.factory', $this->configFactory);
+ $this->container->set('current_user', $this->currentUser);
+ \Drupal::setContainer($this->container);
+
+ // Generate the email message.
+ update_mail($key, $message, $params);
+
+ // Confirm the subject.
+ $this->assertSame("New release(s) available for $site_name", $message['subject']);
+
+ // Confirm each part of the body.
+ if ($authorized) {
+ $this->assertSame($expected_body[0], $message['body'][0]);
+ $this->assertSame($expected_body[1], $message['body'][1]);
+ $this->assertSame($expected_body[2], $message['body'][2]->render());
+ }
+ else {
+ if (empty($params)) {
+ $this->assertSame($expected_body[0], $message['body'][0]);
+ $this->assertSame($expected_body[1], $message['body'][1]->render());
+ }
+ else {
+ $this->assertSame($expected_body[0], $message['body'][0]->render());
+ $this->assertSame($expected_body[1], $message['body'][1]);
+ $this->assertSame($expected_body[2], $message['body'][2]);
+ $this->assertSame($expected_body[3], $message['body'][3]->render());
+ }
+ }
+ }
+
+ /**
+ * Provides data for ::testUpdateEmail.
+ *
+ * @return array
+ * - The value of the update setting 'notification.threshold'.
+ * - An array of parameters for update_mail.
+ * - TRUE if the user is authorized.
+ * - An array of message body strings.
+ */
+ public function providerTestUpdateEmail(): array {
+ return [
+ 'all' => [
+ 'all',
+ [],
+ FALSE,
+ [
+ "See the available updates page for more information:\nhttps://example.com/admin/reports/updates/settings",
+ 'Your site is currently configured to send these emails when any updates are available. To get notified only for security updates, https://example.com/admin/reports/updates.',
+ ],
+ ],
+ 'security' => [
+ 'security',
+ [],
+ FALSE,
+ [
+ "See the available updates page for more information:\nhttps://example.com/admin/reports/updates/settings",
+ 'Your site is currently configured to send these emails only when security updates are available. To get notified for any available updates, https://example.com/admin/reports/updates.',
+ ],
+ ],
+ // Choose parameters that do not require changes to the mocks.
+ 'not secure' => [
+ 'security',
+ [
+ 'core' => UpdateManagerInterface::NOT_SECURE,
+ 'contrib' => NULL,
+ ],
+ FALSE,
+ [
+ "There is a security update available for your version of Drupal. To ensure the security of your server, you should update immediately!",
+ '',
+ "See the available updates page for more information:\nhttps://example.com/admin/reports/updates/settings",
+ "Your site is currently configured to send these emails only when security updates are available. To get notified for any available updates, https://example.com/admin/reports/updates.",
+ ],
+ ],
+ 'authorize' => [
+ 'all',
+ [],
+ TRUE,
+ [
+ "See the available updates page for more information:\nhttps://example.com/admin/reports/updates/settings",
+ "You can automatically download your missing updates using the Update manager:\nhttps://example.com/admin/reports/updates",
+ 'Your site is currently configured to send these emails when any updates are available. To get notified only for security updates, https://example.com/admin/reports/updates.',
+ ],
+ ],
+ ];
+ }
+
+}