diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2ddbade5e..ea5806bff 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -6,16 +6,17 @@ on:
 name: CI
 env:
   SYMFONY_DEPRECATIONS_HELPER: disabled
-  SIMPLETEST_BASE_URL: http://app:8888
+  COMPOSER_DISCARD_CHANGES: true
+  COMPOSER_MIRROR_PATH_REPOS: 1
 jobs:
   tests:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        php-versions: ['8.1', '8.2', '8.3']
+        php-versions: ['8.3']
     container:
-      image: ghcr.io/city-of-helsinki/drupal-php-docker:${{ matrix.php-versions }}-alpine
-      options: --hostname app
+      image: ghcr.io/city-of-helsinki/drupal-web:${{ matrix.php-versions }}-dev
+      options: --hostname app --user 1001
     services:
       db:
         image: mysql:8
@@ -26,6 +27,15 @@ jobs:
           MYSQL_ROOT_PASSWORD: drupal
         ports:
           - 3306:3306
+      chromium:
+        image: selenium/standalone-chromium
+        env:
+          SE_NODE_OVERRIDE_MAX_SESSIONS: "true"
+          SE_NODE_MAX_SESSIONS: "16"
+          SE_START_XVFB: "false"
+          SE_START_VNC: "false"
+          SE_SESSION_RETRY_INTERVAL: "1"
+          SE_SESSION_REQUEST_TIMEOUT: "10"
 
     steps:
       - uses: actions/checkout@v4
@@ -38,6 +48,13 @@ jobs:
       - name: Set Drupal root
         run: echo "DRUPAL_ROOT=$HOME/drupal" >> $GITHUB_ENV
 
+        # Actions worker overrides the default entrypoint with "tail -f /dev/null", so
+        # we have to start services manually.
+      - name: Start services
+        env:
+          WEBROOT: ${{ env.DRUPAL_ROOT }}/public
+        run: entrypoint &
+
       - name: Set module folder
         run: |
           echo "MODULE_FOLDER=$DRUPAL_ROOT/public/modules/contrib/$MODULE_NAME" >> $GITHUB_ENV
@@ -48,23 +65,17 @@ jobs:
           git clone --depth=1 https://github.com/City-of-Helsinki/drupal-helfi-platform.git $DRUPAL_ROOT
           rm -rf $DRUPAL_ROOT/.git
 
+        # We use COMPOSER_MIRROR_PATH_REPOS=1 to mirror local repository
+        # instead of symlinking it to prevent code coverage issues with
+        # phpunit. Copy .git folder manually so codecov can generate line by
+        # line coverage.
       - name: Install required composer dependencies
         working-directory: ${{ env.DRUPAL_ROOT }}
         run: |
           composer config repositories.5 path $GITHUB_WORKSPACE
           composer require drupal/$MODULE_NAME -W
-          # We use COMPOSER_MIRROR_PATH_REPOS=1 to mirror local repository
-          # instead of symlinking it to prevent code coverage issues with
-          # phpunit. Copy .git folder manually so codecov can generate line by
-          # line coverage.
           cp -r $GITHUB_WORKSPACE/.git $MODULE_FOLDER/
 
-      - name: Install Drupal
-        working-directory: ${{ env.DRUPAL_ROOT }}
-        run: |
-          php -d sendmail_path=$(which true); vendor/bin/drush --yes -v site-install minimal --db-url="$SIMPLETEST_DB"
-          vendor/bin/drush en $MODULE_NAME helfi_platform_config_base -y
-
       - name: Run PHPCS
         working-directory: ${{ env.DRUPAL_ROOT }}
         run: vendor/bin/phpcs $MODULE_FOLDER --standard=$MODULE_FOLDER/phpcs.xml --extensions=php,module,inc,install,test,info
@@ -73,9 +84,11 @@ jobs:
         working-directory: ${{ env.DRUPAL_ROOT }}
         run: vendor/bin/phpstan analyze -c $MODULE_FOLDER/phpstan.neon $MODULE_FOLDER
 
-      - name: Start services
+      - name: Install Drupal
         working-directory: ${{ env.DRUPAL_ROOT }}
-        run: vendor/bin/drush runserver $SIMPLETEST_BASE_URL --dns &
+        run: |
+          php -d sendmail_path=$(which true); vendor/bin/drush --yes -v site-install minimal --db-url="$SIMPLETEST_DB"
+          vendor/bin/drush en $MODULE_NAME helfi_platform_config_base -y
 
       - name: Run PHPUnit tests
         working-directory: ${{ env.DRUPAL_ROOT }}
@@ -86,9 +99,12 @@ jobs:
             --coverage-clover=$MODULE_FOLDER/coverage.xml \
             $MODULE_FOLDER
 
-      - name: Run codecov
-        working-directory: ${{ env.MODULE_FOLDER }}
-        run: codecov
+      - uses: codecov/codecov-action@v5
+        with:
+          fail_ci_if_error: true
+          directory: ${{ env.MODULE_FOLDER }}
+          token: ${{ secrets.CODECOV_TOKEN }}
+          verbose: true
 
       - name: Create an artifact from test report
         uses: actions/upload-artifact@v4
diff --git a/modules/hdbt_cookie_banner/tests/modules/hdbt_cookie_banner_test/hdbt_cookie_banner_test.info.yml b/modules/hdbt_cookie_banner/tests/modules/hdbt_cookie_banner_test/hdbt_cookie_banner_test.info.yml
new file mode 100644
index 000000000..7fd1aa085
--- /dev/null
+++ b/modules/hdbt_cookie_banner/tests/modules/hdbt_cookie_banner_test/hdbt_cookie_banner_test.info.yml
@@ -0,0 +1,4 @@
+name: 'HDBT cookie banner test module'
+type: module
+package: Custom
+core_version_requirement: ^10 || ^11
diff --git a/modules/hdbt_cookie_banner/tests/modules/hdbt_cookie_banner_test/hdbt_cookie_banner_test.module b/modules/hdbt_cookie_banner/tests/modules/hdbt_cookie_banner_test/hdbt_cookie_banner_test.module
new file mode 100644
index 000000000..18b44ab4a
--- /dev/null
+++ b/modules/hdbt_cookie_banner/tests/modules/hdbt_cookie_banner_test/hdbt_cookie_banner_test.module
@@ -0,0 +1,18 @@
+<?php
+
+/**
+ * @file
+ * Contains hooks for hdbt cookie banner test module.
+ */
+
+declare(strict_types=1);
+
+/**
+ * Implements hook_page_attachments().
+ */
+function hdbt_cookie_banner_test_page_attachments(array &$attachments) : void {
+  // Alter the HDBT cookie banner settings.
+  $attachments['#attached']['drupalSettings']['hdbt_cookie_banner']['spacerParentSelector'] = '.test-footer';
+  global $base_url;
+  $attachments['#attached']['drupalSettings']['hdbt_cookie_banner']['apiUrl'] = $base_url . '/api/cookie-banner';
+}
diff --git a/modules/hdbt_cookie_banner/tests/modules/hdbt_cookie_banner_test/hdbt_cookie_banner_test.routing.yml b/modules/hdbt_cookie_banner/tests/modules/hdbt_cookie_banner_test/hdbt_cookie_banner_test.routing.yml
new file mode 100644
index 000000000..5a58a5521
--- /dev/null
+++ b/modules/hdbt_cookie_banner/tests/modules/hdbt_cookie_banner_test/hdbt_cookie_banner_test.routing.yml
@@ -0,0 +1,7 @@
+hdbt_cookie_banner_test.test_route:
+  path: '/test-page'
+  defaults:
+    _controller: '\Drupal\hdbt_cookie_banner_test\Controller\TestController::content'
+    _title: 'Test Page'
+  requirements:
+    _permission: 'access content'
diff --git a/modules/hdbt_cookie_banner/tests/modules/hdbt_cookie_banner_test/src/Controller/TestController.php b/modules/hdbt_cookie_banner/tests/modules/hdbt_cookie_banner_test/src/Controller/TestController.php
new file mode 100644
index 000000000..1198c2e4f
--- /dev/null
+++ b/modules/hdbt_cookie_banner/tests/modules/hdbt_cookie_banner_test/src/Controller/TestController.php
@@ -0,0 +1,25 @@
+<?php
+
+namespace Drupal\hdbt_cookie_banner_test\Controller;
+
+use Drupal\Core\Controller\ControllerBase;
+
+/**
+ * Provides a test page for the custom module.
+ */
+class TestController extends ControllerBase {
+
+  /**
+   * Test page content.
+   *
+   * @return array
+   *   Render array.
+   */
+  public function content() {
+    return [
+      '#type' => 'inline_template',
+      '#template' => '<p>Test Content</p><div class="test-footer"></div>',
+    ];
+  }
+
+}
diff --git a/modules/hdbt_cookie_banner/tests/src/FunctionalJavascript/CookieBannerTest.php b/modules/hdbt_cookie_banner/tests/src/FunctionalJavascript/CookieBannerTest.php
new file mode 100644
index 000000000..da5781cad
--- /dev/null
+++ b/modules/hdbt_cookie_banner/tests/src/FunctionalJavascript/CookieBannerTest.php
@@ -0,0 +1,158 @@
+<?php
+
+namespace Drupal\Tests\hdbt_cookie_banner\FunctionalJavascript;
+
+use Behat\Mink\Driver\Selenium2Driver;
+use Drupal\FunctionalJavascriptTests\WebDriverTestBase;
+
+/**
+ * Tests the functionality of the JavaScript cookie banner.
+ *
+ * @group hdbt_cookie_banner
+ */
+class CookieBannerTest extends WebDriverTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'hdbt_cookie_banner',
+    'hdbt_cookie_banner_test',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Setup the test environment.
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Get the path to the JSON file.
+    $module_path = \Drupal::service('extension.list.module')
+      ->getPath('hdbt_cookie_banner');
+    $json_file_path = $module_path . '/assets/json/siteSettingsTemplate.json';
+
+    // Assert the file exists.
+    $this->assertTrue(file_exists($json_file_path));
+
+    // Load and decode the JSON.
+    $json_content = file_get_contents($json_file_path);
+    $this->assertNotEmpty($json_content, 'Decoded JSON data is not empty.');
+
+    // Get the public base URL (in a FunctionalJavascript test).
+    // Construct a URL for the hds-cookie-consent.min.js file.
+    $cookie_js_url = "/$module_path/assets/js/hds-cookie-consent.min.js";
+
+    // Change configuration value before the test runs.
+    $config = $this->config('hdbt_cookie_banner.settings');
+    $config
+      ->set('use_custom_settings', TRUE)
+      ->set('site_settings', $json_content)
+      ->set('use_internal_hds_cookie_js', FALSE)
+      ->set('hds_cookie_js_override', $cookie_js_url)
+      ->save();
+
+    \Drupal::service('cache.default')->deleteAll();
+  }
+
+  /**
+   * Tests the cookie banner visibility and interaction.
+   */
+  public function testCookieBanner() {
+    $this->drupalGet('/test-page');
+    $this->assertSession()->pageTextContains('Test Content');
+    $this->assertSession()->elementExists('css', '.test-footer');
+
+    // Get the web driver.
+    $driver = $this->getSession()->getDriver();
+
+    // Check if the driver is an instance of DrupalSelenium2Driver.
+    if ($driver instanceof Selenium2Driver) {
+      // Get all cookies from the browser.
+      $cookies = $driver->getWebDriverSession()->getCookie();
+
+      // Extract only the 'name' keys from all the cookies, as we want to check
+      // if a specific cookie "change-me" exists.
+      $cookieNames = array_column($cookies, 'name');
+      $this->assertNotContains(
+        'change-me',
+        $cookieNames,
+        'The cookie "change-me" was found, but it should not exist.',
+      );
+    }
+    else {
+      $this->fail('The driver is not an instance of Selenium2Driver.');
+    }
+
+    // Assert that the cookie banner is visible and click the accept button.
+    $this->assertCookieBannerIsVisible();
+
+    // Get the new cookies from the browser.
+    $new_cookies = $driver->getWebDriverSession()->getCookie();
+
+    // There should be a new cookie called "change-me".
+    $cookieNames = array_column($new_cookies, 'name');
+    $this->assertContains(
+      'change-me',
+      $cookieNames,
+      'The cookie "change-me" was not found after clicking the button.',
+    );
+
+    // Reload the page and assert that the cookie banner is not visible.
+    $this->drupalGet('/test-page');
+    $this->assertSession()->pageTextContains('Test Content');
+    $this->assertCookieBannerNotVisible();
+  }
+
+  /**
+   * Asserts that the cookie banner is visible.
+   */
+  protected function assertCookieBannerIsVisible() {
+    // Get the Shadow DOM host and button selectors.
+    $shadowHostSelector = '.hds-cc__target';
+    $buttonSelector = '.hds-cc__all-cookies-button';
+
+    // Verify that the cookie banner is visible and click the accept button.
+    $js = <<<JS
+  const shadowHost = document.querySelector('$shadowHostSelector');
+  if (!shadowHost) {
+    throw new Error('Shadow host not found.');
+  }
+  const shadowRoot = shadowHost.shadowRoot;
+  if (!shadowRoot) {
+    throw new Error('Shadow root is not attached.');
+  }
+  const button = shadowRoot.querySelector('$buttonSelector');
+  if (!button) {
+    throw new Error('Button not found inside the shadow DOM.');
+  }
+  button.click();
+JS;
+
+    // Execute the JavaScript in the browser context.
+    $this->getSession()->executeScript($js);
+  }
+
+  /**
+   * Asserts that the cookie banner is not visible.
+   */
+  protected function assertCookieBannerNotVisible() {
+    // Get the Shadow DOM host and button selectors.
+    $shadowHostSelector = '.hds-cc__target';
+
+    // Verify that the cookie banner is not visible.
+    $js = <<<JS
+  const shadowHost = document.querySelector('$shadowHostSelector');
+  if (shadowHost) {
+    throw new Error('Shadow host still found.');
+  }
+JS;
+    // Execute the JavaScript in the browser context.
+    $this->getSession()->executeScript($js);
+  }
+
+}
diff --git a/phpunit.xml b/phpunit.xml
index 562c1070b..f888cd7ac 100644
--- a/phpunit.xml
+++ b/phpunit.xml
@@ -17,11 +17,10 @@
     <ini name="error_reporting" value="32767"/>
     <!-- Do not limit the amount of memory tests take to run. -->
     <ini name="memory_limit" value="-1"/>
-    <env name="MINK_DRIVER_ARGS_WEBDRIVER" value='["chrome", {"browserName":"chrome","chromeOptions":{"w3c": false, "args":["--disable-gpu","--headless", "--no-sandbox"]}}, "http://127.0.0.1:4444"]' />
-    <env name="DTT_MINK_DRIVER_ARGS" value='["chrome", {"chromeOptions":{"w3c": false }}, "http://chromium:4444"]'/>
-    <env name="DTT_API_OPTIONS" value='{"socketTimeout": 360, "domWaitTimeout": 3600000}' />
+    <env name="MINK_DRIVER_ARGS_WEBDRIVER" value='["chrome", {"browserName":"chrome", "goog:chromeOptions":{"w3c": true, "args":["--no-sandbox", "--ignore-certificate-errors", "--allow-insecure-localhost", "--headless", "--dns-prefetch-disable"]}}, "http://chromium:4444"]' />
+    <env name="DTT_MINK_DRIVER_ARGS" value='["chrome", {"browserName":"chrome", "goog:chromeOptions":{"w3c": true, "args":["--no-sandbox","--ignore-certificate-errors", "--allow-insecure-localhost", "--headless", "--dns-prefetch-disable"]}}, "http://chromium:4444"]'/>    <env name="DTT_API_OPTIONS" value='{"socketTimeout": 360, "domWaitTimeout": 3600000}' />
     <env name="DTT_API_URL" value="http://chromium:9222"/>
-    <env name="DTT_BASE_URL" value="http://app:8888"/>
+    <env name="DTT_BASE_URL" value="https://app"/>
   </php>
   <testsuites>
     <testsuite name="unit">