Issue #1905070: Port test to Drupal 8.

Fix fails along the way and create a config schema so that I can test
properly.

config/schema/fillpdf.schema.yml

+fillpdf.settings:
+  type: config_object
+  mapping:
+    remote_protocol:
+      type: string
+      label: 'FillPDF Service endpoint protocol'
+    remote_endpoint:
+      type: string
+      label: 'FillPDF Service endpoint URL without protocol'
+    scheme:
+      type: string
+      label: 'Filesystem scheme for uploads'

fillpdf.info.yml

@@ -10,3 +10,4 @@ dependencies:
   - token
   - views
   - serialization
+  - options

src/Form/FillPdfOverviewForm.php

@@ -6,6 +6,7 @@
 
 namespace Drupal\fillpdf\Form;
 
+use Drupal\Component\Render\FormattableMarkup;
 use Drupal\Core\Entity\Query\QueryFactory;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\File\FileSystemInterface;
@@ -109,7 +110,7 @@ class FillPdfOverviewForm extends FillPdfAdminFormBase {
         ];
       }
       else {
-        drupal_set_message($this->t('You must install the <a href="@xmlrpc">contributed XML-RPC module</a> in order to use FillPDF Service as your PDF-filling method.', [
+        drupal_set_message($this->t('You must install the <a href=":xmlrpc">contributed XML-RPC module</a> in order to use FillPDF Service as your PDF-filling method.', [
           '@xmlrpc' => Url::fromUri('https://drupal.org/project/xmlrpc')
             ->toString(),
         ]), 'error');
@@ -117,7 +118,7 @@ class FillPdfOverviewForm extends FillPdfAdminFormBase {
     }
     else {
       $form['message'] = [
-        '#markup' => '<p>' . $this->t('Before you can upload PDF files, you must !link.', ['!link' => $this->l($this->t('configure FillPDF'), Url::fromRoute('fillpdf.settings'))]) . '</p>',
+        '#markup' => '<p>' . $this->t('Before you can upload PDF files, you must @link.', ['@link' => new FormattableMarkup($this->l($this->t('configure FillPDF'), Url::fromRoute('fillpdf.settings')), [])]) . '</p>',
       ];
       drupal_set_message($this->t('FillPDF is not configured.'), 'error');
     }

src/Tests/FillPdfOverviewFormTest.php

+<?php
+/**
+ * @file fillpdf.test
+ * Contains tests for the module.
+ */
+
+namespace Drupal\fillpdf\Tests;
+
+use Drupal\Core\Url;
+use Drupal\simpletest\WebTestBase;
+
+/**
+ * Ensure the overview form at /admin/structure/fillpdf functions correctly.
+ *
+ * @ingroup fillpdf
+ *
+ * @group fillpdf
+ */
+class FillPdfOverviewFormTest extends WebTestBase {
+
+  static public $modules = ['fillpdf'];
+  protected $profile = 'minimal';
+
+  public function testUploadForm() {
+    // Create and log in our privileged user.
+    $user = $this->createUser([
+      'access administration pages',
+      'administer pdfs',
+    ]);
+    $this->drupalLogin($user);
+
+    $this->drupalGet(Url::fromRoute('fillpdf.forms_admin'));
+  }
+
+}
+