Resolve #3448583 "Add tests for"

Closes #3448583

tests/src/Functional/GroupContextDomainBrowserTestBase.php

+<?php
+
+namespace Drupal\Tests\group_context_domain\Functional;
+
+use Drupal\Tests\group\Functional\GroupBrowserTestBase;
+use Drupal\Tests\group_context_domain\Traits\GroupContextDomainTestTrait;
+
+/**
+ * Provides a base class for Group Context: Domain functional tests.
+ */
+abstract class GroupContextDomainBrowserTestBase extends GroupBrowserTestBase {
+
+  use GroupContextDomainTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['domain', 'group_context_domain'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+}