diff --git a/core/modules/image/src/Entity/ImageStyle.php b/core/modules/image/src/Entity/ImageStyle.php
index 1239c9720f..bdf8f805e0 100644
--- a/core/modules/image/src/Entity/ImageStyle.php
+++ b/core/modules/image/src/Entity/ImageStyle.php
@@ -229,7 +229,6 @@ public function transformDimensions(array &$dimensions, $uri) {
       ->dispatch(ImageDerivativePipelineEvents::RESOLVE_DERIVATIVE_IMAGE_DIMENSIONS);
     $dimensions['width'] = $pipeline->getVariable('derivativeImageWidth');
     $dimensions['height'] = $pipeline->getVariable('derivativeImageHeight');
-    return;
   }
 
   /**
diff --git a/core/modules/image/tests/src/Functional/ImageDimensionsTest.php b/core/modules/image/tests/src/Functional/ImageDimensionsTest.php
index 70f271504c..3564782887 100644
--- a/core/modules/image/tests/src/Functional/ImageDimensionsTest.php
+++ b/core/modules/image/tests/src/Functional/ImageDimensionsTest.php
@@ -347,7 +347,7 @@ public function testImageDimensions() {
     $this->assertSame('<img src="' . $url . '" width="120" height="60" alt="" class="image-style-test" />', $this->getImageTag($variables));
     $this->assertFileNotExists($generated_uri, 'Generated file does not exist.');
     $this->drupalGet($this->getAbsoluteUrl($url));
-    $this->assertResponse(200, 'Image was generated at the URL.');
+    $this->assertSession()->statusCodeEquals(200);
     $this->assertFileExists($generated_uri, 'Generated file does exist after we accessed it.');
     $image_file = $image_factory->get($generated_uri);
     $this->assertSame(120, $image_file->getWidth());
@@ -368,7 +368,7 @@ public function testImageDimensions() {
     $this->assertSame('<img src="' . $url . '" width="60" height="120" alt="" class="image-style-test" />', $this->getImageTag($variables));
     $this->assertFileNotExists($generated_uri, 'Generated file does not exist.');
     $this->drupalGet($this->getAbsoluteUrl($url));
-    $this->assertResponse(200, 'Image was generated at the URL.');
+    $this->assertSession()->statusCodeEquals(200);
     $this->assertFileExists($generated_uri, 'Generated file does exist after we accessed it.');
     $image_file = $image_factory->get($generated_uri);
     $this->assertSame(60, $image_file->getWidth());
@@ -390,7 +390,7 @@ public function testImageDimensions() {
     $this->assertSame('<img src="' . $url . '" width="45" height="90" alt="" class="image-style-test" />', $this->getImageTag($variables));
     $this->assertFileNotExists($generated_uri, 'Generated file does not exist.');
     $this->drupalGet($this->getAbsoluteUrl($url));
-    $this->assertResponse(200, 'Image was generated at the URL.');
+    $this->assertSession()->statusCodeEquals(200);
     $this->assertFileExists($generated_uri, 'Generated file does exist after we accessed it.');
     $image_file = $image_factory->get($generated_uri);
     $this->assertSame(45, $image_file->getWidth());
@@ -412,7 +412,7 @@ public function testImageDimensions() {
     $this->assertSame('<img src="' . $url . '" width="45" height="90" alt="" class="image-style-test" />', $this->getImageTag($variables));
     $this->assertFileNotExists($generated_uri, 'Generated file does not exist.');
     $this->drupalGet($this->getAbsoluteUrl($url));
-    $this->assertResponse(200, 'Image was generated at the URL.');
+    $this->assertSession()->statusCodeEquals(200);
     $this->assertFileExists($generated_uri, 'Generated file does exist after we accessed it.');
     $image_file = $image_factory->get($generated_uri);
     $this->assertSame(45, $image_file->getWidth());
@@ -430,7 +430,7 @@ public function testImageDimensions() {
     $this->assertSame('<img src="' . $url . '" width="45" height="90" alt="" class="image-style-test" />', $this->getImageTag($variables));
     $this->assertFileNotExists($generated_uri, 'Generated file does not exist.');
     $this->drupalGet($this->getAbsoluteUrl($url));
-    $this->assertResponse(200, 'Image was generated at the URL.');
+    $this->assertSession()->statusCodeEquals(200);
     $this->assertFileExists($generated_uri, 'Generated file does exist after we accessed it.');
     $image_file = $image_factory->get($generated_uri);
     $this->assertSame(45, $image_file->getWidth());
@@ -451,7 +451,7 @@ public function testImageDimensions() {
     $this->assertSame('<img src="' . $url . '" alt="" class="image-style-test" />', $this->getImageTag($variables));
     $this->assertFileNotExists($generated_uri, 'Generated file does not exist.');
     $this->drupalGet($this->getAbsoluteUrl($url));
-    $this->assertResponse(200, 'Image was generated at the URL.');
+    $this->assertSession()->statusCodeEquals(200);
     $this->assertFileExists($generated_uri, 'Generated file does exist after we accessed it.');
 
     // Add a crop effect.
@@ -470,7 +470,7 @@ public function testImageDimensions() {
     $this->assertEqual('<img src="' . $url . '" width="30" height="30" alt="" class="image-style-test" />', $this->getImageTag($variables));
     $this->assertFileNotExists($generated_uri, 'Generated file does not exist.');
     $this->drupalGet($this->getAbsoluteUrl($url));
-    $this->assertResponse(200, 'Image was generated at the URL.');
+    $this->assertSession()->statusCodeEquals(200);
     $this->assertFileExists($generated_uri, 'Generated file does exist after we accessed it.');
     $image_file = $image_factory->get($generated_uri);
     $this->assertSame(30, $image_file->getWidth());
@@ -493,7 +493,7 @@ public function testImageDimensions() {
     // $this->assertSame('<img src="' . $url . '" width="41" height="41" alt="" class="image-style-test" />', $this->getImageTag($variables));
     $this->assertFileNotExists($generated_uri, 'Generated file does not exist.');
     $this->drupalGet($this->getAbsoluteUrl($url));
-    $this->assertResponse(200, 'Image was generated at the URL.');
+    $this->assertSession()->statusCodeEquals(200);
     $this->assertFileExists($generated_uri, 'Generated file does exist after we accessed it.');
     $image_file = $image_factory->get($generated_uri);
     // @todo Uncomment this once
@@ -541,7 +541,7 @@ public function testImageDimensions() {
     $this->assertSame('<img src="' . $url . '" width="100" height="100" alt="" class="image-style-test-uri" />', $this->getImageTag($variables));
     $this->assertFileNotExists($generated_uri, 'Generated file does not exist.');
     $this->drupalGet($this->getAbsoluteUrl($url));
-    $this->assertResponse(200, 'Image was generated at the URL.');
+    $this->assertSession()->statusCodeEquals(200);
     $this->assertFileExists($generated_uri, 'Generated file does exist after we accessed it.');
     $image_file = $image_factory->get($generated_uri);
     $this->assertSame(100, $image_file->getWidth());
@@ -558,7 +558,7 @@ public function testImageDimensions() {
     $this->assertSame('<img src="' . $url . '" width="50" height="50" alt="" class="image-style-test-uri" />', $this->getImageTag($variables));
     $this->assertFileNotExists($generated_uri, 'Generated file does not exist.');
     $this->drupalGet($this->getAbsoluteUrl($url));
-    $this->assertResponse(200, 'Image was generated at the URL.');
+    $this->assertSession()->statusCodeEquals(200);
     $this->assertFileExists($generated_uri, 'Generated file does exist after we accessed it.');
     $image_file = $image_factory->get($generated_uri);
     $this->assertSame(50, $image_file->getWidth());
diff --git a/core/modules/image/tests/src/Functional/ImageStylesPathAndUrlTest.php b/core/modules/image/tests/src/Functional/ImageStylesPathAndUrlTest.php
index 8632f5dbdf..8d4176dbd4 100644
--- a/core/modules/image/tests/src/Functional/ImageStylesPathAndUrlTest.php
+++ b/core/modules/image/tests/src/Functional/ImageStylesPathAndUrlTest.php
@@ -402,7 +402,7 @@ public function testImageStyleUrlForMissingSourceImage() {
       ->getDerivativeImageUrl()
       ->toString();
     $this->drupalGet($generated_url);
-    $this->assertResponse(404, 'Accessing an image style URL with a source image that does not exist provides a 404 error response.');
+    $this->assertSession()->statusCodeEquals(404);
   }
 
   /**
@@ -490,10 +490,10 @@ public function testImageStyleUrlAndPath(string $scheme, bool $clean_url, bool $
 
     // Add some extra chars to the token.
     $this->drupalGet(str_replace(IMAGE_DERIVATIVE_TOKEN . '=', IMAGE_DERIVATIVE_TOKEN . '=Zo', $generate_url));
-    $this->assertResponse(404, 'Image was inaccessible at the URL with an invalid token.');
+    $this->assertSession()->statusCodeEquals(404);
     // Change the parameter name so the token is missing.
     $this->drupalGet(str_replace(IMAGE_DERIVATIVE_TOKEN . '=', 'wrongparam=', $generate_url));
-    $this->assertResponse(404, 'Image was inaccessible at the URL with a missing token.');
+    $this->assertSession()->statusCodeEquals(404);
 
     // Check that the generated URL is the same when we pass in a relative path
     // rather than a URI. We need to temporarily switch the default scheme to
@@ -511,7 +511,7 @@ public function testImageStyleUrlAndPath(string $scheme, bool $clean_url, bool $
 
     // Fetch the URL that generates the file.
     $this->drupalGet($generate_url);
-    $this->assertResponse(200, 'Image was generated at the URL.');
+    $this->assertSession()->statusCodeEquals(200);
     $this->assertFileExists($generated_uri);
     // assertRaw can't be used with string containing non UTF-8 chars.
     $this->assertNotEmpty(file_get_contents($generated_uri), 'URL returns expected file.');
@@ -532,7 +532,7 @@ public function testImageStyleUrlAndPath(string $scheme, bool $clean_url, bool $
       // Make sure that a second request to the already existing derivative
       // works too.
       $this->drupalGet($generate_url);
-      $this->assertResponse(200, 'Image was generated at the URL.');
+      $this->assertSession()->statusCodeEquals(200);
 
       // Check that the second request also returned the generated image.
       $this->assertSame($image->getFileSize(), (int) $this->drupalGetHeader('Content-Length'));
@@ -544,7 +544,7 @@ public function testImageStyleUrlAndPath(string $scheme, bool $clean_url, bool $
       // have access.
       \Drupal::state()->delete('image.test_file_download');
       $this->drupalGet($generate_url);
-      $this->assertResponse(403, 'Confirmed that access is denied for the private image style.');
+      $this->assertSession()->statusCodeEquals(403);
 
       // Repeat this with a different file that we do not have access to and
       // make sure that access is denied.
@@ -558,7 +558,7 @@ public function testImageStyleUrlAndPath(string $scheme, bool $clean_url, bool $
       $generate_url_noaccess = $pipeline->getDerivativeImageUrl()->toString();
 
       $this->drupalGet($generate_url_noaccess);
-      $this->assertResponse(403, 'Confirmed that access is denied for the private image style.');
+      $this->assertSession()->statusCodeEquals(403);
       // Verify that images are not appended to the response.
       // Currently this test only uses PNG images.
       $this->assertStringContainsString('.png', $generate_url, 'Confirming that private image styles are not appended require PNG file.');
@@ -575,7 +575,7 @@ public function testImageStyleUrlAndPath(string $scheme, bool $clean_url, bool $
       if ($clean_url) {
         // Add some extra chars to the token.
         $this->drupalGet(str_replace(IMAGE_DERIVATIVE_TOKEN . '=', IMAGE_DERIVATIVE_TOKEN . '=Zo', $generate_url));
-        $this->assertResponse(200, 'Existing image was accessible at the URL with an invalid token.');
+        $this->assertSession()->statusCodeEquals(200);
       }
     }
 
@@ -606,7 +606,7 @@ public function testImageStyleUrlAndPath(string $scheme, bool $clean_url, bool $
     $generate_url = $pipeline->getDerivativeImageUrl()->toString();
     $this->assertStringNotContainsString(IMAGE_DERIVATIVE_TOKEN . '=', $generate_url, 'The security token does not appear in the image style URL.');
     $this->drupalGet($generate_url);
-    $this->assertResponse(200, 'Image was accessible at the URL with a missing token.');
+    $this->assertSession()->statusCodeEquals(200);
 
     // Stop suppressing the security token in the URL.
     $this->config('image.settings')->set('suppress_itok_output', FALSE)->save();
@@ -623,16 +623,16 @@ public function testImageStyleUrlAndPath(string $scheme, bool $clean_url, bool $
     $this->assertTrue($matches_expected_url_format, "URL for a derivative of an image style matches expected format.");
     $nested_url_with_wrong_token = str_replace(IMAGE_DERIVATIVE_TOKEN . '=', 'wrongparam=', $nested_url);
     $this->drupalGet($nested_url_with_wrong_token);
-    $this->assertResponse(404, 'Image generated from an earlier derivative was inaccessible at the URL with a missing token.');
+    $this->assertSession()->statusCodeEquals(404);
     // Check that this restriction cannot be bypassed by adding extra slashes
     // to the URL.
     $this->drupalGet(substr_replace($nested_url_with_wrong_token, '//styles/', strrpos($nested_url_with_wrong_token, '/styles/'), strlen('/styles/')));
-    $this->assertResponse(404, 'Image generated from an earlier derivative was inaccessible at the URL with a missing token, even with an extra forward slash in the URL.');
+    $this->assertSession()->statusCodeEquals(404);
     $this->drupalGet(substr_replace($nested_url_with_wrong_token, '////styles/', strrpos($nested_url_with_wrong_token, '/styles/'), strlen('/styles/')));
-    $this->assertResponse(404, 'Image generated from an earlier derivative was inaccessible at the URL with a missing token, even with multiple forward slashes in the URL.');
+    $this->assertSession()->statusCodeEquals(404);
     // Make sure the image can still be generated if a correct token is used.
     $this->drupalGet($nested_url);
-    $this->assertResponse(200, 'Image was accessible when a correct token was provided in the URL.');
+    $this->assertSession()->statusCodeEquals(200);
 
     // Check that requesting a nonexistent image does not create any new
     // directories in the file system.
diff --git a/core/modules/image/tests/src/Kernel/DerivativeImageProcessTest.php b/core/modules/image/tests/src/Kernel/DerivativeImageProcessTest.php
index 5f9627be9f..98b277efb1 100644
--- a/core/modules/image/tests/src/Kernel/DerivativeImageProcessTest.php
+++ b/core/modules/image/tests/src/Kernel/DerivativeImageProcessTest.php
@@ -138,7 +138,7 @@ public function testBuildDerivativeImageFromFile() {
       ->setImageStyle($this->imageStyle)
       ->setSourceImageUri('public://test.png');
     $this->assertTrue($pipeline->buildDerivativeImage());
-    $this->assertTrue(file_exists('public://styles/thumbnail/public/test.png'));
+    $this->assertFileExists('public://styles/thumbnail/public/test.png');
     $image = \Drupal::service('image.factory')->get('public://styles/thumbnail/public/test.png');
     $this->assertSame(100, $image->getWidth());
     $this->assertSame(67, $image->getHeight());
@@ -148,14 +148,14 @@ public function testBuildDerivativeImageFromFile() {
       ->setImageStyle($this->imageStyle)
       ->setSourceImageUri('public://missing.png');
     $this->assertFalse($pipeline->buildDerivativeImage());
-    $this->assertFalse(file_exists('public://styles/thumbnail/public/missing.png'));
+    $this->assertFileNotExists('public://styles/thumbnail/public/missing.png');
 
     // Starting off from a path.
     $pipeline = $this->imageProcessor->createInstance('derivative')
       ->setImageStyle($this->imageStyle)
       ->setSourceImageUri('core/modules/image/sample.png');
     $this->assertTrue($pipeline->buildDerivativeImage());
-    $this->assertTrue(file_exists('public://styles/thumbnail/public/core/modules/image/sample.png'));
+    $this->assertFileExists('public://styles/thumbnail/public/core/modules/image/sample.png');
     $image = \Drupal::service('image.factory')->get('public://styles/thumbnail/public/core/modules/image/sample.png');
     $this->assertSame(100, $image->getWidth());
     $this->assertSame(75, $image->getHeight());
@@ -192,7 +192,7 @@ public function testBuildDerivativeImageFromImageObject() {
     $this->assertTrue($pipeline->buildDerivativeImage());
 
     // Check if derivative image exists.
-    $this->assertTrue(file_exists($derivative_uri));
+    $this->assertFileExists($derivative_uri);
 
     // Check derivative image after saving, with old object.
     $this->assertSame(100, $image->getWidth());