diff --git a/core/modules/system/src/Plugin/ImageToolkit/GDToolkit.php b/core/modules/system/src/Plugin/ImageToolkit/GDToolkit.php
index 394ffb347e..a772913e9f 100644
--- a/core/modules/system/src/Plugin/ImageToolkit/GDToolkit.php
+++ b/core/modules/system/src/Plugin/ImageToolkit/GDToolkit.php
@@ -249,7 +249,7 @@ public function save($destination) {
     }
     else {
       // Image types that support alpha need to be saved accordingly.
-      if (in_array($this->getType(), [IMAGETYPE_PNG, IMAGETYPE_WEBP])) {
+      if (in_array($this->getType(), [IMAGETYPE_PNG, IMAGETYPE_WEBP], TRUE)) {
         imagealphablending($this->getResource(), FALSE);
         imagesavealpha($this->getResource(), TRUE);
       }
@@ -458,12 +458,8 @@ public function extensionToImageType($extension) {
    *   An array of available image types. An image type is represented by a PHP
    *   IMAGETYPE_* constant (e.g. IMAGETYPE_JPEG, IMAGETYPE_PNG, etc.).
    */
-  public static function supportedTypes() {
-    $supported_types = [IMAGETYPE_PNG, IMAGETYPE_JPEG, IMAGETYPE_GIF];
-    if (function_exists('imagewebp')) {
-      $supported_types[] = IMAGETYPE_WEBP;
-    }
-    return $supported_types;
+  protected static function supportedTypes() {
+    return [IMAGETYPE_PNG, IMAGETYPE_JPEG, IMAGETYPE_GIF, IMAGETYPE_WEBP];
   }
 
 }
diff --git a/core/tests/Drupal/KernelTests/Core/Image/ToolkitGdTest.php b/core/tests/Drupal/KernelTests/Core/Image/ToolkitGdTest.php
index 6c5b32d4aa..b597627141 100644
--- a/core/tests/Drupal/KernelTests/Core/Image/ToolkitGdTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Image/ToolkitGdTest.php
@@ -108,14 +108,8 @@ public function testManipulations() {
     // Test that the image factory is set to use the GD toolkit.
     $this->assertEqual($this->imageFactory->getToolkitId(), 'gd', 'The image factory is set to use the \'gd\' image toolkit.');
 
-    // Get a blank Image object.
-    $image = $this->imageFactory->get();
-
     // Test the list of supported extensions.
-    $expected_extensions = ['png', 'gif', 'jpeg', 'jpg', 'jpe'];
-    if (in_array(IMAGETYPE_WEBP, $image->getToolkit()->supportedTypes())) {
-      $expected_extensions[] = 'webp';
-    }
+    $expected_extensions = ['png', 'gif', 'jpeg', 'jpg', 'jpe', 'webp'];
     $supported_extensions = $this->imageFactory->getSupportedExtensions();
     $this->assertEqual($expected_extensions, array_intersect($expected_extensions, $supported_extensions));
 
@@ -127,10 +121,9 @@ public function testManipulations() {
       'jpeg' => IMAGETYPE_JPEG,
       'jpg' => IMAGETYPE_JPEG,
       'jpe' => IMAGETYPE_JPEG,
+      'webp' => IMAGETYPE_WEBP,
     ];
-    if (in_array(IMAGETYPE_WEBP, $image->getToolkit()->supportedTypes())) {
-      $expected_image_types['webp'] = IMAGETYPE_WEBP;
-    }
+    $image = $this->imageFactory->get();
     foreach ($expected_image_types as $extension => $expected_image_type) {
       $image_type = $image->getToolkit()->extensionToImageType($extension);
       $this->assertSame($expected_image_type, $image_type);
@@ -146,10 +139,8 @@ public function testManipulations() {
       'image-test.gif',
       'image-test-no-transparency.gif',
       'image-test.jpg',
+      'img-test.webp',
     ];
-    if (in_array(IMAGETYPE_WEBP, $image->getToolkit()->supportedTypes())) {
-      $files[] = 'img-test.webp';
-    }
 
     // Setup a list of tests to perform on each type.
     $operations = [
@@ -223,18 +214,14 @@ public function testManipulations() {
         'arguments' => ['extension' => 'png'],
         'corners' => $default_corners,
       ],
+      'convert_webp' => [
+        'function' => 'convert',
+        'width' => 40,
+        'height' => 20,
+        'arguments' => ['extension' => 'webp'],
+        'corners' => $default_corners,
+      ],
     ];
-    if (in_array(IMAGETYPE_WEBP, $image->getToolkit()->supportedTypes())) {
-      $operations += [
-        'convert_webp' => [
-          'function' => 'convert',
-          'width' => 40,
-          'height' => 20,
-          'arguments' => ['extension' => 'webp'],
-          'corners' => $default_corners,
-        ],
-      ];
-    }
 
     // Systems using non-bundled GD2 don't have imagerotate. Test if available.
     // @todo Remove the version check once
@@ -396,9 +383,8 @@ public function testManipulations() {
             // conversion. The convert operation cannot handle that correctly.
             if ($image->getToolkit()->getType() == $image_original_type || $corner != $this->transparent) {
               $correct_colors = $this->colorsAreEqual($color, $corner);
-              $actual_color = implode(',', $color);
-              $expected_color = implode(',', $corner);
-              $this->assertTrue($correct_colors, "Color of image '{$file}' after '{$op}' operation at corner {$key} is ({$actual_color}), expected ({$expected_color}).");
+              $this->assertTrue($correct_colors, new FormattableMarkup('Image %file object after %action action has the correct color placement at corner %corner.',
+                ['%file' => $file, '%action' => $op, '%corner' => $key]));
             }
           }
         }
@@ -410,7 +396,7 @@ public function testManipulations() {
     }
 
     // Test creation of image from scratch, and saving to storage.
-    foreach ($image->getToolkit()->supportedTypes() as $type) {
+    foreach ([IMAGETYPE_PNG, IMAGETYPE_GIF, IMAGETYPE_JPEG, IMAGETYPE_WEBP] as $type) {
       $image = $this->imageFactory->get();
       $image->createNew(50, 20, image_type_to_extension($type, FALSE), '#ffff00');
       $file = 'from_null' . image_type_to_extension($type);