diff --git a/tests/src/Functional/FillPdfSettingsFormTest.php b/tests/src/Functional/FillPdfSettingsFormTest.php
index 7ac85dfb5b3e0c7c25f1b9127b5159d3a0ade395..02cf2f7f9833ddadb379e6e45a78a0b9d9967e87 100644
--- a/tests/src/Functional/FillPdfSettingsFormTest.php
+++ b/tests/src/Functional/FillPdfSettingsFormTest.php
@@ -27,6 +27,11 @@ class FillPdfSettingsFormTest extends BrowserTestBase {
    */
   protected $strictConfigSchema = FALSE;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/tests/src/Functional/PdfParseTest.php b/tests/src/Functional/PdfParseTest.php
index b2fa8fb636fb2bdb3e189dd3b782560b5f47fca6..58f2d3f06feeac2f94bf2bc52bcb8cea4f6fd785 100644
--- a/tests/src/Functional/PdfParseTest.php
+++ b/tests/src/Functional/PdfParseTest.php
@@ -27,7 +27,7 @@ class PdfParseTest extends FillPdfTestBase {
 
     $config = $this->config('fillpdf.settings');
     if (!FillPdf::checkLocalServiceEndpoint($this->container->get('http_client'), $config)) {
-      throw new \PHPUnit_Framework_SkippedTestError('FillPDF LocalServer unavailable, so skipping test.');
+      $this->markTestSkipped('FillPDF LocalServer unavailable, so skipping test.');
     }
 
     $this->backendTest($config);
@@ -44,7 +44,7 @@ class PdfParseTest extends FillPdfTestBase {
     $this->configureFillPdf(['backend' => 'pdftk']);
 
     if (!FillPdf::checkPdftkPath()) {
-      throw new \PHPUnit_Framework_SkippedTestError('pdftk not available, so skipping test.');
+      $this->markTestSkipped('pdftk not available, so skipping test.');
     }
 
     $this->backendTest($this->config('fillpdf.settings'));
diff --git a/tests/src/Functional/PdfPopulationTest.php b/tests/src/Functional/PdfPopulationTest.php
index d46475fc35c06bb7410500bc19d6d13a334fdd64..82cb207fcc4cd881841e441fbddaa1741597b044 100644
--- a/tests/src/Functional/PdfPopulationTest.php
+++ b/tests/src/Functional/PdfPopulationTest.php
@@ -295,7 +295,6 @@ class PdfPopulationTest extends FillPdfTestBase {
   /**
    * Tests PDF population using local service.
    *
-   * @throws \PHPUnit_Framework_SkippedTestError
    * @throws \Behat\Mink\Exception\ResponseTextException
    *   Thrown when test had to be skipped as FillPDF LocalServer is not
    *   available.
@@ -310,7 +309,7 @@ class PdfPopulationTest extends FillPdfTestBase {
     $this->configureLocalServiceBackend();
     $config = $this->container->get('config.factory')->get('fillpdf.settings');
     if (!FillPdf::checkLocalServiceEndpoint($this->container->get('http_client'), $config)) {
-      throw new \PHPUnit_Framework_SkippedTestError('FillPDF LocalServer unavailable, so skipping test.');
+      $this->markTestSkipped('FillPDF LocalServer unavailable, so skipping test.');
     }
     $this->backendTest();
   }
@@ -318,7 +317,6 @@ class PdfPopulationTest extends FillPdfTestBase {
   /**
    * Tests PDF population using a local install of pdftk.
    *
-   * @throws \PHPUnit_Framework_SkippedTestError
    * @throws \Behat\Mink\Exception\ResponseTextException
    *   Thrown when test had to be skipped as local pdftk install is not
    *   available.
@@ -326,7 +324,7 @@ class PdfPopulationTest extends FillPdfTestBase {
   public function testMergePdftk() {
     $this->configureFillPdf(['backend' => 'pdftk']);
     if (!FillPdf::checkPdftkPath()) {
-      throw new \PHPUnit_Framework_SkippedTestError('pdftk not available, so skipping test.');
+      $this->markTestSkipped('pdftk not available, so skipping test.');
     }
     $this->backendTest();
   }
diff --git a/tests/src/Functional/PdfWebformPopulationTest.php b/tests/src/Functional/PdfWebformPopulationTest.php
index b29d24612d97414c71394d494dfacfcdd0f7a67f..b6fcb3aac691e1ac7ba68f9119fea7922d0a16e0 100644
--- a/tests/src/Functional/PdfWebformPopulationTest.php
+++ b/tests/src/Functional/PdfWebformPopulationTest.php
@@ -42,7 +42,7 @@ class PdfWebformPopulationTest extends FillPdfTestBase {
   /**
    * {@inheritdoc}
    */
-  protected function setUp(): void {
+  protected function setUp() {
     // @todo: Stop skipping this test when Webform has Drupal 9 support.
     if (version_compare('9.0.0', \Drupal::VERSION, '>=')) {
       $this->markTestSkipped('Webform is not yet compatible with Drupal 9, so skipping these tests.');