diff --git a/core/modules/system/tests/src/Functional/System/SitesDirectoryHardeningTest.php b/core/modules/system/tests/src/Functional/System/SitesDirectoryHardeningTest.php
index 78e220e12e7..b8b25652d7f 100644
--- a/core/modules/system/tests/src/Functional/System/SitesDirectoryHardeningTest.php
+++ b/core/modules/system/tests/src/Functional/System/SitesDirectoryHardeningTest.php
@@ -65,8 +65,10 @@ class SitesDirectoryHardeningTest extends BrowserTestBase {
     $this->assertStringContainsString('settings.php is not protected from modifications and poses a security risk.', $description);
     $this->assertStringContainsString('services.yml is not protected from modifications and poses a security risk.', $description);
 
-    $this->assertTrue(is_writable($site_path), 'Site directory remains writable when automatically fixing permissions is disabled.');
-    $this->assertTrue(is_writable($settings_file), 'settings.php remains writable when automatically fixing permissions is disabled.');
+    // Verify that site directory and the settings.php remain writable when
+    // automatically enforcing file permissions is disabled.
+    $this->assertDirectoryIsWritable($site_path);
+    $this->assertFileIsWritable($settings_file);
 
     // Re-enable permissions enforcement.
     $settings = Settings::getAll();
@@ -77,8 +79,10 @@ class SitesDirectoryHardeningTest extends BrowserTestBase {
     $requirements = $this->checkSystemRequirements();
     $this->assertEquals('Protected', (string) $requirements['configuration_files']['value']);
 
-    $this->assertFalse(is_writable($site_path), 'Site directory is protected when automatically fixing permissions is enabled.');
-    $this->assertFalse(is_writable($settings_file), 'settings.php is protected when automatically fixing permissions is enabled.');
+    // Verify that site directory and the settings.php remain protected when
+    // automatically enforcing file permissions is enabled.
+    $this->assertDirectoryNotIsWritable($site_path);
+    $this->assertFileNotIsWritable($settings_file);
   }
 
   /**
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerSkipPermissionHardeningTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerSkipPermissionHardeningTest.php
index 13dec4b97f6..aa81b33e7f1 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerSkipPermissionHardeningTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerSkipPermissionHardeningTest.php
@@ -27,8 +27,8 @@ class InstallerSkipPermissionHardeningTest extends InstallerTestBase {
    */
   protected function setUpSite() {
     $site_directory = $this->container->getParameter('app.root') . '/' . $this->siteDirectory;
-    $this->assertTrue(is_writable($site_directory));
-    $this->assertTrue(is_writable($site_directory . '/settings.php'));
+    $this->assertDirectoryIsWritable($site_directory);
+    $this->assertFileIsWritable($site_directory . '/settings.php');
 
     $this->assertSession()->responseContains('All necessary changes to <em class="placeholder">' . $this->siteDirectory . '</em> and <em class="placeholder">' . $this->siteDirectory . '/settings.php</em> have been made, so you should remove write permissions to them now in order to avoid security risks. If you are unsure how to do so, consult the <a href="https://www.drupal.org/server-permissions">online handbook</a>.');
 
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerTest.php
index 570354028cf..b3ad2445292 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerTest.php
@@ -95,8 +95,8 @@ class InstallerTest extends InstallerTestBase {
     // Test that SiteConfigureForm::buildForm() has made the site directory and
     // the settings file non-writable.
     $site_directory = $this->container->getParameter('app.root') . '/' . $this->siteDirectory;
-    $this->assertFalse(is_writable($site_directory));
-    $this->assertFalse(is_writable($site_directory . '/settings.php'));
+    $this->assertDirectoryNotIsWritable($site_directory);
+    $this->assertFileNotIsWritable($site_directory . '/settings.php');
 
     parent::setUpSite();
   }
diff --git a/core/tests/Drupal/Tests/Core/Image/ImageTest.php b/core/tests/Drupal/Tests/Core/Image/ImageTest.php
index c7b5769e4c8..f9c899e5b36 100644
--- a/core/tests/Drupal/Tests/Core/Image/ImageTest.php
+++ b/core/tests/Drupal/Tests/Core/Image/ImageTest.php
@@ -188,7 +188,7 @@ class ImageTest extends UnitTestCase {
   public function testIsValid() {
     $this->getTestImage(FALSE);
     $this->assertTrue($this->image->isValid());
-    $this->assertTrue(is_readable($this->image->getSource()));
+    $this->assertFileIsReadable($this->image->getSource());
   }
 
   /**