Issue #3393105 & #2708615: Added Turbo JavaScript alter kernel test.

modules/refreshless_turbo/tests/refreshless_turbo_test/js/alter_already_header.js

+(function () {
+  // Empty lololol.
+})();

modules/refreshless_turbo/tests/refreshless_turbo_test/js/alter_basic.js

+(function () {
+  // Empty lololol.
+})();

modules/refreshless_turbo/tests/refreshless_turbo_test/refreshless_turbo_test.info.yml

+name: RefreshLess - Turbo - Test module
+type: module
+description: Test module for the RefreshLess <a href="https://turbo.hotwired.dev/">Hotwire Turbo library</a>.
+package: Testing
+core_version_requirement: ^10.1
+php: 8.1

modules/refreshless_turbo/tests/refreshless_turbo_test/refreshless_turbo_test.libraries.yml

+alter_basic:
+  js:
+    js/alter_basic.js: {}
+
+alter_already_header:
+  js:
+    js/alter_already_header.js: {}
+  header: true

modules/refreshless_turbo/tests/src/Kernel/JavascriptAlterTest.php

+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\refreshless_turbo\Kernel;
+
+use Drupal\Core\Asset\AttachedAssets;
+use Drupal\Core\Asset\AssetResolverInterface;
+use Drupal\Core\Language\LanguageManagerInterface;
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * Tests that JavaScript libraries are altered as needed for Turbo.
+ *
+ * Note that at the time of writing with Hux 1.2, discovery of hook classes
+ * seems to only work if they're defined in self::$modules but for whatever
+ * reason they don't get discovered as hooks if the module containing the hook
+ * classes is enabled after that point; KernelTestBase::enableModules() does
+ * not cause them to be discovered, nor does installing the modules via the
+ * 'module_installer' service; forcing a container rebuild doesn't work, nor
+ * does deleting various caches such as 'cache.bootstrap'. Because of this, we
+ * can't do a before and after comparison in the test, and ultimately what
+ * matters is that no JavaScript is left in the footer but is instead found in
+ * the header.
+ *
+ * @group refreshless
+ *
+ * @group refreshless_turbo
+ *
+ * @coversDefaultClass \Drupal\refreshless_turbo\Hooks\Javascript
+ *
+ * @see \Drupal\KernelTests\Core\Asset\AttachedAssetsTest::testAddFiles()
+ *
+ * @see \Drupal\KernelTests\Core\Asset\AttachedAssetsTest::testAlter()
+ *
+ * @see https://www.drupal.org/project/hux/issues/3401023
+ *   Hux issue opened as part of writing this test with the above problem.
+ */
+class JavascriptAlterTest extends KernelTestBase {
+
+  /**
+   * The Drupal asset resolver service.
+   *
+   * @var \Drupal\Core\Asset\AssetResolverInterface
+   */
+  protected readonly AssetResolverInterface $assetResolver;
+
+  /**
+   * The Drupal language manager.
+   *
+   * @var \Drupal\Core\Language\LanguageManagerInterface
+   */
+  protected readonly LanguageManagerInterface $languageManager;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'hux', 'refreshless', 'refreshless_turbo', 'refreshless_turbo_test',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+
+    parent::setUp();
+
+    $this->assetResolver    = $this->container->get('asset.resolver');
+    $this->languageManager  = $this->container->get('language_manager');
+
+  }
+
+  /**
+   * Test that our alter hook forces our test JavaScript into header + defer.
+   *
+   * @covers ::alter
+   */
+  public function testAlterBasic(): void {
+
+    $build = ['#attached' => ['library' => [
+      'refreshless_turbo_test/alter_basic',
+    ]]];
+
+    /** @var \Drupal\Core\Asset\AttachedAssetsInterface Attached assets collection. */
+    $assets = AttachedAssets::createFromRenderArray($build);
+
+    /** @var array[] Array containing resolved header and footer JavaScript. */
+    $javascript = $this->assetResolver->getJsAssets(
+      $assets, false, $this->languageManager->getCurrentLanguage(),
+    );
+
+    // Header should not be empty.
+    $this->assertNotEmpty($javascript[0]);
+
+    $this->assertCount(1, $javascript[0]);
+
+    // Footer should be completely empty.
+    $this->assertEmpty($javascript[1]);
+
+    $entry = \reset($javascript[0]);
+
+    $this->assertArrayHasKey('attributes', $entry);
+
+    $this->assertArrayHasKey('defer', $entry['attributes']);
+
+    $this->assertTrue($entry['attributes']['defer']);
+
+  }
+
+  /**
+   * Test that our alter hook leaves test JavaScript alone if already in header.
+   *
+   * @covers ::alter
+   */
+  public function testAlterAlreadyHeader(): void {
+
+    $build = ['#attached' => ['library' => [
+      'refreshless_turbo_test/alter_already_header',
+    ]]];
+
+    /** @var \Drupal\Core\Asset\AttachedAssetsInterface Attached assets collection. */
+    $assets = AttachedAssets::createFromRenderArray($build);
+
+    /** @var array[] Array containing resolved header and footer JavaScript. */
+    $javascript = $this->assetResolver->getJsAssets(
+      $assets, false, $this->languageManager->getCurrentLanguage(),
+    );
+
+    // Header should not be empty.
+    $this->assertNotEmpty($javascript[0]);
+
+    $this->assertCount(1, $javascript[0]);
+
+    // Footer should be completely empty.
+    $this->assertEmpty($javascript[1]);
+
+    $entry = \reset($javascript[0]);
+
+    // The 'attributes' key should always exist but we didn't set the 'defer'
+    // attribute in the library definition so we expect 'defer' to not exist.
+    $this->assertArrayNotHasKey('defer', $entry['attributes']);
+
+  }
+
+  /**
+   * Test that our alter hook forces core JavaScript into the header.
+   *
+   * @covers ::alter
+   */
+  public function testAlterCore(): void {
+
+    $build = ['#attached' => ['library' => [
+      'core/drupal.ajax',
+      'core/drupal.announce',
+      'core/drupal.message',
+    ]]];
+
+    /** @var \Drupal\Core\Asset\AttachedAssetsInterface Attached assets collection. */
+    $assets = AttachedAssets::createFromRenderArray($build);
+
+    /** @var array[] Array containing resolved header and footer JavaScript. */
+    $javascript = $this->assetResolver->getJsAssets(
+      $assets, false, $this->languageManager->getCurrentLanguage(),
+    );
+
+    // Header should not be empty.
+    $this->assertNotEmpty($javascript[0]);
+
+    $this->assertArrayHasKey('core/misc/ajax.js',     $javascript[0]);
+    $this->assertArrayHasKey('core/misc/announce.js', $javascript[0]);
+    $this->assertArrayHasKey('core/misc/message.js',  $javascript[0]);
+
+    // Footer should be completely empty.
+    $this->assertEmpty($javascript[1]);
+
+  }
+
+}