diff -u b/tests/src/Functional/ReadOnlyConfigTest.php b/tests/src/Functional/ReadOnlyConfigTest.php
--- b/tests/src/Functional/ReadOnlyConfigTest.php
+++ b/tests/src/Functional/ReadOnlyConfigTest.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\Tests\config_readonly\Functional;
 
+use Behat\Mink\Element\NodeElement;
 use Drupal\Tests\BrowserTestBase;
 use Drupal\Core\Url;
 
@@ -31,7 +32,7 @@
    *
    * @var string
    */
-  public $message = 'This form will not be saved because the configuration active store is read-only.';
+  private $message = 'This form will not be saved because the configuration active store is read-only.';
 
   /**
    * {@inheritdoc}
@@ -86,7 +87,7 @@
     $edit = [
       'modules[Core][action][enable]' => 'action',
     ];
-    $this->drupalPostForm($module_url, $edit, t('Install'));
+    $this->drupalPostForm($module_url, $edit, 'Install');
     $this->assertSession()->pageTextNotContains($this->message);
 
     // Switch forms to read-only.
@@ -100,9 +101,9 @@
 
     $this->drupalGet($module_url);
     $elements = $this->xpath("//form[@id='system-modules']//input[@id='edit-submit']");
-//    $install_button = isset($elements[0]) && $elements[0] instanceof \SimpleXMLElement ? $elements[0]-> attributes() : FALSE;
-//    self::assertTrue($install_button !== FALSE, 'Found the install form submit button.');
-//    self::assertTrue((string) $install_button['disabled'] == 'disabled', 'The install modules form button is disabled.');
+    $install_button = isset($elements[0]) && $elements[0] instanceof NodeElement ? $elements[0] : FALSE;
+    $this->assertTrue($install_button !== FALSE, 'Found the install form submit button.');
+    $this->assertTrue($install_button->hasAttribute('disabled'), 'The install modules form button is disabled.');
   }
 
   /**