Issue #3451951: Added a test to check if the toolbar 'Content' tab has the .content css class.

Closes #3451951

tests/src/Functional/TestMenuCssNames.php

+<?php
+
+namespace Drupal\Tests\menu_css_names\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests the menu_css_names module.
+ *
+ * @group menu_css_names
+ */
+class TestMenuCssNames extends BrowserTestBase {
+
+  /**
+   * Modules to install.
+   *
+   * @var array
+   */
+  protected static $modules = [
+    'node',
+    'toolbar',
+    'menu_css_names',
+  ];
+
+  /**
+   * The default theme.
+   *
+   * @var string
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * A simple user.
+   *
+   * @var \Drupal\user\UserInterface
+   */
+  private $user;
+
+  /**
+   * Perform initial setup tasks that run before every test method.
+   */
+  public function setUp(): void {
+    parent::setUp();
+    $this->user = $this->drupalCreateUser([
+      'access toolbar',
+      'access content overview',
+    ]);
+    $this->drupalLogin($this->user);
+  }
+
+  /**
+   * Tests that the Content admin toolbar css class is present.
+   */
+  public function testClassExists() {
+    $this->drupalGet('/');
+    $this->assertSession()->statusCodeEquals(200);
+
+    // Check if the "Content" admin toolbar css class is present.
+    $this->assertSession()->elementExists('css', 'li.content');
+  }
+
+}