UHF-8909: Added Kernel test for default language variables.

src/Language/DefaultLanguageResolver.php

@@ -11,7 +11,7 @@
 /**
  * Resolves default languages and fallbacks.
  */
-final class DefaultLanguageResolver implements DefaultLanguageResolverInterface {
+final class DefaultLanguageResolver {
 
   /**
    * Constructs a new instance.

tests/src/Kernel/Language/DefaultLanguageVariablesTest.php

@@ -0,0 +1,40 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\helfi_api_base\Kernel\Language;
+
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * Tests helfi_api_base_template_preprocess_default_variables_alter().
+ *
+ * @group helfi_api_base
+ */
+class DefaultLanguageVariablesTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'helfi_api_base',
+  ];
+
+  /**
+   * Test helfi_api_base_template_preprocess_default_variables_alter().
+   */
+  public function testDefaultLanguageVariables(): void {
+    // Prepare variables for the page template.
+    $render_array = [
+      '#theme' => 'page',
+      '#content' => ['#markup' => 'Test content'],
+    ];
+    \Drupal::moduleHandler()->alter('template_preprocess_default_variables', $render_array);
+    \Drupal::moduleHandler()->invokeAll('preprocess_page', [&$render_array]);
+
+    // Check if variables are set correctly.
+    $this->assertInstanceOf('Drupal\Core\Language\Language', $render_array['language']);
+    $this->assertNotNull($render_array['alternative_language']);
+  }
+
+}