diff --git a/core/modules/toolbar/tests/src/Functional/ToolbarIntegrationTest.php b/core/modules/toolbar/tests/src/Functional/ToolbarIntegrationTest.php
index 0e3a8ec..cc6fe96 100644
--- a/core/modules/toolbar/tests/src/Functional/ToolbarIntegrationTest.php
+++ b/core/modules/toolbar/tests/src/Functional/ToolbarIntegrationTest.php
@@ -22,14 +22,33 @@ class ToolbarIntegrationTest extends JavascriptTestBase {
   public static $modules = ['toolbar', 'node'];
 
   public function testToolbarToggling() {
-    $admin_user = $this->drupalCreateUser(['access toolbar', 'administer site configuration', 'access content overview']);
+    $admin_user = $this->drupalCreateUser([
+      'access toolbar',
+      'administer site configuration',
+      'access content overview'
+    ]);
     $this->drupalLogin($admin_user);
 
     $this->drupalGet('<front>');
-    $this->assertTrue($this->getSession()->getDriver()->isVisible('.//a[@id="toolbar-link-system-admin_content"]'), 'Toolbar not open by default');
 
+    // Test that it is possible to toggle the toolbar tray.
+    $this->assertTrue($this->getSession()->getDriver()->isVisible('.//a[@id="toolbar-link-system-admin_content"]'), 'Toolbar tray is open by default.');
     $this->getSession()->getDriver()->click('.//a[@id="toolbar-item-administration"]');
-    $this->assertFalse($this->getSession()->getDriver()->isVisible('//a[@id="toolbar-link-system-admin_content"]'), 'Toolbar not closed after clicking manage');
+    $this->assertFalse($this->getSession()->getDriver()->isVisible('//a[@id="toolbar-link-system-admin_content"]'), 'Toolbar tray is closed after clicking the "Manage" button.');
+    $this->getSession()->getDriver()->click('.//a[@id="toolbar-item-administration"]');
+    $this->assertTrue($this->getSession()->getDriver()->isVisible('//a[@id="toolbar-link-system-admin_content"]'), 'Toolbar tray is visible again after clicking the "Manage" button a second time.');
+
+    // Test toggling the toolbar tray between horizontal and vertical.
+    $this->assertTrue($this->getSession()->getDriver()->isVisible('.//div[@id="toolbar-item-administration-tray" and contains(concat(" ", @class, " "), " toolbar-tray-horizontal ")]'), 'Toolbar tray is horizontally oriented by default.');
+    $this->assertEmpty($this->getSession()->getDriver()->find('.//div[@id="toolbar-item-administration-tray" and contains(concat(" ", @class, " "), " toolbar-tray-vertical ")]'), 'Toolbar tray not vertically oriented by default.');
+
+    $this->getSession()->getDriver()->click('.//div[@id="toolbar-item-administration-tray"]//button[contains(concat(" ", @class, " "), " toolbar-icon-toggle-vertical ")]');
+    $this->assertTrue($this->getSession()->getDriver()->wait(1000, 'jQuery("#toolbar-item-administration-tray").hasClass("toolbar-tray-vertical")'));
+    $this->assertTrue($this->getSession()->getDriver()->isVisible('.//div[@id="toolbar-item-administration-tray" and contains(concat(" ", @class, " "), " toolbar-tray-vertical ")]'), 'After toggling the orientation the toolbar tray is now displayed vertically.');
+
+    $this->getSession()->getDriver()->click('.//div[@id="toolbar-item-administration-tray"]//button[contains(concat(" ", @class, " "), " toolbar-icon-toggle-horizontal ")]');
+    $this->assertTrue($this->getSession()->getDriver()->wait(1000, 'jQuery("#toolbar-item-administration-tray").hasClass("toolbar-tray-horizontal")'));
+    $this->assertTrue($this->getSession()->getDriver()->isVisible('.//div[@id="toolbar-item-administration-tray" and contains(concat(" ", @class, " "), " toolbar-tray-horizontal ")]'), 'After toggling the orientation a second time the toolbar tray is displayed horizontally again.');
   }
 
 }