diff --git a/core/modules/simpletest/files/img-test.webp b/core/modules/simpletest/files/img-test.webp
deleted file mode 100644
index c9c799c..0000000
Binary files a/core/modules/simpletest/files/img-test.webp and /dev/null differ
diff --git a/core/tests/Drupal/KernelTests/Core/Image/ToolkitGdTest.php b/core/tests/Drupal/KernelTests/Core/Image/ToolkitGdTest.php
index a7fb86f..2fae80f 100644
--- a/core/tests/Drupal/KernelTests/Core/Image/ToolkitGdTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Image/ToolkitGdTest.php
@@ -52,11 +52,6 @@ protected function setUp() {
 
     // Set the image factory service.
     $this->imageFactory = $this->container->get('image.factory');
-
-    // For PHP 7.1+, ensure test PHP has webp extension installed.
-    if (PHP_VERSION_ID >= 70100) {
-      $this->assertTrue(function_exists('imagewebp'));
-    }
   }
 
   protected function checkRequirements() {
@@ -70,6 +65,23 @@ protected function checkRequirements() {
   }
 
   /**
+   * Builds a WebP format test image using GD primitives.
+   */
+  protected function buildWebpTestImage() {
+    $res = imagecreatetruecolor(40, 20);
+    $red = imagecolorallocatealpha($res, 255, 0, 0, 0);
+    $green = imagecolorallocatealpha($res, 0, 255, 0, 0);
+    $blue = imagecolorallocatealpha($res, 0, 0, 255, 0);
+    $yellow_transparent = imagecolorallocatealpha($res, 255, 255, 0, 127);
+    imagefilledrectangle($res, 0, 0, 19, 9, $red);
+    imagefilledrectangle($res, 20, 0, 39, 9, $green);
+    imagefilledrectangle($res, 20, 10, 39, 19, $blue);
+    imagefilledrectangle($res, 0, 10, 19, 19, $yellow_transparent);
+    imagesavealpha($res, TRUE);
+    imagewebp($res, Settings::get('file_public_path') . '/sourceimagetest/img-test.webp');
+  }
+
+  /**
    * Function to compare two colors by RGBa.
    */
   function colorsAreEqual($color_a, $color_b) {
@@ -151,9 +163,6 @@ function testManipulations() {
       'image-test-no-transparency.gif',
       'image-test.jpg',
     );
-    if ($image->getToolkit()->isWebpSupported()) {
-      $files[] = 'img-test.webp';
-    }
 
     // Setup a list of tests to perform on each type.
     $operations = array(
@@ -295,6 +304,17 @@ function testManipulations() {
       );
     }
 
+    // Prepare a directory with source test images.
+    $directory = Settings::get('file_public_path') . '/sourceimagetest';
+    file_prepare_directory($directory, FILE_CREATE_DIRECTORY);
+    foreach ($files as $file) {
+      file_unmanaged_copy(drupal_get_path('module', 'simpletest') . '/files/' . $file, $directory, FILE_EXISTS_RENAME);
+    }
+    if ($image->getToolkit()->isWebpSupported()) {
+      $this->buildWebpTestImage();
+      $files[] = 'img-test.webp';
+    }
+
     // Prepare a directory for test file results.
     $directory = Settings::get('file_public_path') . '/imagetest';
     file_prepare_directory($directory, FILE_CREATE_DIRECTORY);
@@ -302,7 +322,7 @@ function testManipulations() {
     foreach ($files as $file) {
       foreach ($operations as $op => $values) {
         // Load up a fresh image.
-        $image = $this->imageFactory->get(drupal_get_path('module', 'simpletest') . '/files/' . $file);
+        $image = $this->imageFactory->get(Settings::get('file_public_path') . '/sourceimagetest/' . $file);
         $toolkit = $image->getToolkit();
         if (!$image->isValid()) {
           $this->fail(SafeMarkup::format('Could not load image %file.', array('%file' => $file)));