diff --git a/src/Form/ConfigForm.php b/src/Form/ConfigForm.php
index 284e54d9..87a32058 100644
--- a/src/Form/ConfigForm.php
+++ b/src/Form/ConfigForm.php
@@ -10,6 +10,8 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
+declare(strict_types=1);
+
 namespace Drupal\collabora_online\Form;
 
 use Drupal\Core\Form\ConfigFormBase;
@@ -25,14 +27,14 @@ class ConfigForm extends ConfigFormBase {
   /**
    * {@inheritdoc}
    */
-  public function getFormId() {
+  public function getFormId(): string {
     return 'collabora_configform';
   }
 
   /**
    * {@inheritdoc}
    */
-  public function getEditableConfigNames() {
+  public function getEditableConfigNames(): array {
     return [
       static::SETTINGS,
     ];
@@ -41,47 +43,50 @@ public function getEditableConfigNames() {
   /**
    * {@inheritdoc}
    */
-  public function buildForm(array $form, FormStateInterface $form_state) {
+  public function buildForm(array $form, FormStateInterface $form_state): array {
     $config = $this->config(static::SETTINGS);
+    $cool_settings = $config->get('cool');
 
     $form['server'] = [
-      '#type' => 'textfield',
+      '#type' => 'url',
       '#title' => $this->t('Collabora Online server URL'),
-      '#default_value' => $config->get('cool')['server'],
+      '#default_value' => $cool_settings['server'] ?? '',
       '#required' => TRUE,
     ];
 
     $form['wopi_base'] = [
-      '#type' => 'textfield',
-      '#title' => $this->t('WOPI host URL. Likely https://<drupal_server>'),
-      '#default_value' => $config->get('cool')['wopi_base'],
+      '#type' => 'url',
+      '#title' => $this->t('WOPI host URL'),
+      '#description' => $this->t('Likely https://<drupal_server>'),
+      '#default_value' => $cool_settings['wopi_base'] ?? '',
       '#required' => TRUE,
     ];
 
     $form['key_id'] = [
       '#type' => 'textfield',
       '#title' => $this->t('JWT private key ID'),
-      '#default_value' => $config->get('cool')['key_id'],
+      '#default_value' => $cool_settings['key_id'] ?? '',
       '#required' => TRUE,
     ];
 
     $form['access_token_ttl'] = [
-      '#type' => 'textfield',
+      '#type' => 'number',
       '#title' => $this->t('Access Token Expiration (in seconds)'),
-      '#default_value' => $config->get('cool')['access_token_ttl'],
+      '#default_value' => $cool_settings['access_token_ttl'] ?? 0,
+      '#min' => 0,
       '#required' => TRUE,
     ];
 
     $form['disable_cert_check'] = [
       '#type' => 'checkbox',
       '#title' => $this->t('Disable TLS certificate check for COOL.'),
-      '#default_value' => $config->get('cool')['disable_cert_check'],
+      '#default_value' => $cool_settings['disable_cert_check'] ?? FALSE,
     ];
 
     $form['allowfullscreen'] = [
       '#type' => 'checkbox',
       '#title' => $this->t('Allow COOL to use fullscreen mode.'),
-      '#default_value' => $config->get('cool')['allowfullscreen'] ?? FALSE,
+      '#default_value' => $cool_settings['allowfullscreen'] ?? FALSE,
     ];
 
     return parent::buildForm($form, $form_state);
@@ -90,12 +95,21 @@ public function buildForm(array $form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
-  public function submitForm(array &$form, FormStateInterface $form_state) {
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    // Remove slashes at the end of wopi_base URL.
     $wopi_base = rtrim($form_state->getValue('wopi_base'), '/');
+    $form_state->setValueForElement($form['wopi_base'], $wopi_base);
 
+    parent::validateForm($form, $form_state);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state): void {
     $this->config(static::SETTINGS)
       ->set('cool.server', $form_state->getValue('server'))
-      ->set('cool.wopi_base', $wopi_base)
+      ->set('cool.wopi_base', $form_state->getValue('wopi_base'))
       ->set('cool.key_id', $form_state->getValue('key_id'))
       ->set('cool.access_token_ttl', $form_state->getValue('access_token_ttl'))
       ->set('cool.disable_cert_check', $form_state->getValue('disable_cert_check'))
diff --git a/tests/src/Functional/ConfigFormTest.php b/tests/src/Functional/ConfigFormTest.php
new file mode 100644
index 00000000..bbf7329c
--- /dev/null
+++ b/tests/src/Functional/ConfigFormTest.php
@@ -0,0 +1,128 @@
+<?php
+
+/*
+ * Copyright the Collabora Online contributors.
+ *
+ * SPDX-License-Identifier: MPL-2.0
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\collabora_online\Functional;
+
+use Drupal\Core\Url;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests the Collabora configuration.
+ */
+class ConfigFormTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'collabora_online',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Tests the configuration for the Collabora settings form.
+   */
+  public function testConfigForm(): void {
+    $assert_session = $this->assertSession();
+
+    // User without permission can't access the configuration page.
+    $this->drupalGet(Url::fromRoute('collabora-online.settings'));
+    $assert_session->pageTextContains('You are not authorized to access this page.');
+    $assert_session->statusCodeEquals(403);
+
+    // User with permission can access the configuration page.
+    $user = $this->createUser(['administer site configuration']);
+    $this->drupalLogin($user);
+    $this->drupalGet(Url::fromRoute('collabora-online.settings'));
+    $assert_session->statusCodeEquals(200);
+
+    // The form contains default values from module install.
+    $this->drupalGet(Url::fromRoute('collabora-online.settings'));
+    $assert_session->fieldValueEquals('Collabora Online server URL', 'https://localhost:9980/');
+    $assert_session->fieldValueEquals('WOPI host URL', 'https://localhost/');
+    $assert_session->fieldValueEquals('JWT private key ID', 'cool');
+    $assert_session->fieldValueEquals('Access Token Expiration (in seconds)', '86400');
+    $assert_session->fieldValueEquals('Disable TLS certificate check for COOL.', '');
+    $assert_session->fieldValueEquals('Allow COOL to use fullscreen mode.', '1');
+
+    // Change the form values, then submit the form.
+    $assert_session->fieldExists('Collabora Online server URL')
+      ->setValue('http://collaboraserver.com/');
+    $assert_session->fieldExists('WOPI host URL')
+      ->setValue('http://wopihost.com/');
+    $assert_session->fieldExists('JWT private key ID')
+      ->setValue('name_of_a_key');
+    $assert_session->fieldExists('Access Token Expiration (in seconds)')
+      ->setValue('3600');
+    $assert_session->fieldExists('Disable TLS certificate check for COOL.')
+      ->check();
+    // Since default is checked we disable the full screen option.
+    $assert_session->fieldExists('Allow COOL to use fullscreen mode.')
+      ->uncheck();
+    $assert_session->buttonExists('Save configuration')->press();
+    $assert_session->statusMessageContains('The configuration options have been saved.', 'status');
+
+    // The settings have been updated.
+    $this->drupalGet(Url::fromRoute('collabora-online.settings'));
+    $assert_session->fieldValueEquals('Collabora Online server URL', 'http://collaboraserver.com/');
+    // Slash is removed at the end of Wopi URL.
+    $assert_session->fieldValueEquals('WOPI host URL', 'http://wopihost.com');
+    $assert_session->fieldValueEquals('JWT private key ID', 'name_of_a_key');
+    $assert_session->fieldValueEquals('Access Token Expiration (in seconds)', '3600');
+    $assert_session->fieldValueEquals('Disable TLS certificate check for COOL.', '1');
+    $assert_session->fieldValueEquals('Allow COOL to use fullscreen mode.', '');
+
+    // Test validation of required fields.
+    $this->drupalGet(Url::fromRoute('collabora-online.settings'));
+    $assert_session->fieldExists('Collabora Online server URL')->setValue('');
+    $assert_session->fieldExists('WOPI host URL')->setValue('');
+    $assert_session->fieldExists('JWT private key ID')->setValue('');
+    $assert_session->fieldExists('Access Token Expiration (in seconds)')->setValue('');
+    $assert_session->fieldExists('Disable TLS certificate check for COOL.')->uncheck();
+    $assert_session->fieldExists('Allow COOL to use fullscreen mode.')->uncheck();
+    $assert_session->buttonExists('Save configuration')->press();
+    $assert_session->statusMessageContains('Collabora Online server URL field is required.', 'error');
+    $assert_session->statusMessageContains('WOPI host URL field is required.', 'error');
+    $assert_session->statusMessageContains('JWT private key ID field is required.', 'error');
+    $assert_session->statusMessageContains('Access Token Expiration (in seconds) field is required.', 'error');
+
+    // Test validation of bad form values.
+    $this->drupalGet(Url::fromRoute('collabora-online.settings'));
+    // Set invalid value for URL fields.
+    $assert_session->fieldExists('Collabora Online server URL')->setValue('/internal');
+    $assert_session->fieldExists('WOPI host URL')->setValue('any-other-value');
+    // Set invalid values for numeric field.
+    $assert_session->fieldExists('Access Token Expiration (in seconds)')->setValue('text');
+    $assert_session->buttonExists('Save configuration')->press();
+    $assert_session->statusMessageContains('The URL /internal is not valid.', 'error');
+    $assert_session->statusMessageContains('The URL any-other-value is not valid.', 'error');
+    $assert_session->statusMessageNotContains('Access Token Expiration (in seconds) must be a number.', 'status');
+
+    // Test form with no configuration.
+    \Drupal::configFactory()->getEditable('collabora_online.settings')->setData([])->save();
+    $this->drupalGet(Url::fromRoute('collabora-online.settings'));
+    $assert_session->fieldValueEquals('Collabora Online server URL', '');
+    $assert_session->fieldValueEquals('WOPI host URL', '');
+    $assert_session->fieldValueEquals('JWT private key ID', '');
+    $assert_session->fieldValueEquals('Access Token Expiration (in seconds)', '0');
+    $assert_session->fieldValueEquals('Disable TLS certificate check for COOL.', '');
+    $assert_session->fieldValueEquals('Allow COOL to use fullscreen mode.', '');
+    $assert_session->buttonExists('Save configuration');
+  }
+
+}
diff --git a/tests/src/Kernel/MediaHelperTest.php b/tests/src/Kernel/MediaHelperTest.php
index 8f371ddc..d92d62ac 100644
--- a/tests/src/Kernel/MediaHelperTest.php
+++ b/tests/src/Kernel/MediaHelperTest.php
@@ -1,5 +1,15 @@
 <?php
 
+/*
+ * Copyright the Collabora Online contributors.
+ *
+ * SPDX-License-Identifier: MPL-2.0
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
 declare(strict_types=1);
 
 namespace Drupal\Tests\collabora_online\Kernel;