diff --git a/includes/validation/class-amp-validation-error-taxonomy.php b/includes/validation/class-amp-validation-error-taxonomy.php
index 29fccdaaf69..8a6501b67cd 100644
--- a/includes/validation/class-amp-validation-error-taxonomy.php
+++ b/includes/validation/class-amp-validation-error-taxonomy.php
@@ -3344,6 +3344,10 @@ public static function get_source_key_label( $key, $validation_error ) {
 				return __( 'Invalid attribute', 'amp' );
 			case 'required_attr_value':
 				return __( 'Required attribute value', 'amp' );
+			case 'url':
+				return __( 'URL', 'amp' );
+			case 'message':
+				return __( 'Message', 'amp' );
 			default:
 				return $key;
 		}
diff --git a/lib/common/phpstan.neon.dist b/lib/common/phpstan.neon.dist
index 1857a8b4809..fb2b62bf871 100644
--- a/lib/common/phpstan.neon.dist
+++ b/lib/common/phpstan.neon.dist
@@ -8,3 +8,5 @@ parameters:
 		- %currentWorkingDirectory%/src/
 	autoload_files:
 		- %currentWorkingDirectory%/vendor/autoload.php
+	ignoreErrors:
+		- '#^PHPDoc tag @throws with type AmpProject\\Exception\\FailedRemoteRequest is not subtype of Throwable$#'
diff --git a/lib/common/src/Exception/FailedRemoteRequest.php b/lib/common/src/Exception/FailedRemoteRequest.php
new file mode 100644
index 00000000000..0a03765943b
--- /dev/null
+++ b/lib/common/src/Exception/FailedRemoteRequest.php
@@ -0,0 +1,13 @@
+<?php
+
+namespace AmpProject\Exception;
+
+/**
+ * Marker interface to enable consumers to catch all exceptions for failed remote requests.
+ *
+ * @package ampproject/common
+ */
+interface FailedRemoteRequest extends AmpException
+{
+
+}
diff --git a/lib/common/src/Exception/FailedToGetCachedResponse.php b/lib/common/src/Exception/FailedToGetCachedResponse.php
new file mode 100644
index 00000000000..8ac4ab32bd1
--- /dev/null
+++ b/lib/common/src/Exception/FailedToGetCachedResponse.php
@@ -0,0 +1,27 @@
+<?php
+
+namespace AmpProject\Exception;
+
+use RuntimeException;
+
+/**
+ * Exception thrown when a cached remote response could not be retrieved.
+ *
+ * @package ampproject/common
+ */
+final class FailedToGetCachedResponse extends RuntimeException implements FailedRemoteRequest
+{
+
+    /**
+     * Instantiate a FailedToGetCachedResponseData exception for a URL if the cached response data could not be retrieved.
+     *
+     * @param string $url URL that failed to be fetched.
+     * @return self
+     */
+    public static function withUrl($url)
+    {
+        $message = "Failed to retrieve the cached response for the URL '{$url}'.";
+
+        return new self($message);
+    }
+}
diff --git a/lib/common/src/Exception/FailedToGetFromRemoteUrl.php b/lib/common/src/Exception/FailedToGetFromRemoteUrl.php
index 8383c4e8fd4..015d1dca6b6 100644
--- a/lib/common/src/Exception/FailedToGetFromRemoteUrl.php
+++ b/lib/common/src/Exception/FailedToGetFromRemoteUrl.php
@@ -10,7 +10,7 @@
  *
  * @package ampproject/common
  */
-final class FailedToGetFromRemoteUrl extends RuntimeException implements AmpException
+final class FailedToGetFromRemoteUrl extends RuntimeException implements FailedRemoteRequest
 {
 
     /**
diff --git a/lib/common/src/RemoteGetRequest.php b/lib/common/src/RemoteGetRequest.php
index 0469eb1db2d..9d96ec11daa 100644
--- a/lib/common/src/RemoteGetRequest.php
+++ b/lib/common/src/RemoteGetRequest.php
@@ -2,7 +2,7 @@
 
 namespace AmpProject;
 
-use AmpProject\Exception\FailedToGetFromRemoteUrl;
+use AmpProject\Exception\FailedRemoteRequest;
 
 /**
  * Interface for abstracting away the transport that is being used for making remote requests.
@@ -19,7 +19,7 @@ interface RemoteGetRequest
      *
      * @param string $url URL to get.
      * @return Response Response for the executed request.
-     * @throws FailedToGetFromRemoteUrl If retrieving the contents from the URL failed.
+     * @throws FailedRemoteRequest If retrieving the contents from the URL failed.
      */
     public function get($url);
 }
diff --git a/lib/common/src/RemoteRequest/CurlRemoteGetRequest.php b/lib/common/src/RemoteRequest/CurlRemoteGetRequest.php
index 8a6528d01da..940ed6974d9 100644
--- a/lib/common/src/RemoteRequest/CurlRemoteGetRequest.php
+++ b/lib/common/src/RemoteRequest/CurlRemoteGetRequest.php
@@ -2,6 +2,7 @@
 
 namespace AmpProject\RemoteRequest;
 
+use AmpProject\Exception\FailedRemoteRequest;
 use AmpProject\Exception\FailedToGetFromRemoteUrl;
 use AmpProject\RemoteGetRequest;
 use AmpProject\Response;
@@ -92,7 +93,7 @@ public function __construct($sslVerify = true, $timeout = self::DEFAULT_TIMEOUT,
      *
      * @param string $url URL to get.
      * @return Response Response for the executed request.
-     * @throws FailedToGetFromRemoteUrl If retrieving the contents from the URL failed.
+     * @throws FailedRemoteRequest If retrieving the contents from the URL failed.
      */
     public function get($url)
     {
diff --git a/lib/common/src/RemoteRequest/FallbackRemoteGetRequest.php b/lib/common/src/RemoteRequest/FallbackRemoteGetRequest.php
index 95f6d86a088..d6a36fe1de8 100644
--- a/lib/common/src/RemoteRequest/FallbackRemoteGetRequest.php
+++ b/lib/common/src/RemoteRequest/FallbackRemoteGetRequest.php
@@ -2,7 +2,7 @@
 
 namespace AmpProject\RemoteRequest;
 
-use AmpProject\Exception\FailedToGetFromRemoteUrl;
+use AmpProject\Exception\FailedRemoteRequest;
 use AmpProject\RemoteGetRequest;
 use AmpProject\Response;
 use Exception;
@@ -55,7 +55,7 @@ private function addRemoteGetRequestInstance(RemoteGetRequest $remoteGetRequest)
      *
      * @param string $url URL to get.
      * @return Response Response for the executed request.
-     * @throws FailedToGetFromRemoteUrl If retrieving the contents from the URL failed.
+     * @throws FailedRemoteRequest If retrieving the contents from the URL failed.
      */
     public function get($url)
     {
diff --git a/lib/common/src/RemoteRequest/FilesystemRemoteGetRequest.php b/lib/common/src/RemoteRequest/FilesystemRemoteGetRequest.php
index baf0028ca5b..00b0ef7e3ae 100644
--- a/lib/common/src/RemoteRequest/FilesystemRemoteGetRequest.php
+++ b/lib/common/src/RemoteRequest/FilesystemRemoteGetRequest.php
@@ -2,6 +2,7 @@
 
 namespace AmpProject\RemoteRequest;
 
+use AmpProject\Exception\FailedRemoteRequest;
 use AmpProject\Exception\FailedToGetFromRemoteUrl;
 use AmpProject\RemoteGetRequest;
 use AmpProject\Response;
@@ -40,7 +41,7 @@ public function __construct($argumentMap)
      *
      * @param string $url URL to get.
      * @return Response Response for the executed request.
-     * @throws FailedToGetFromRemoteUrl If retrieving the contents from the URL failed.
+     * @throws FailedRemoteRequest If retrieving the contents from the URL failed.
      */
     public function get($url)
     {
diff --git a/lib/common/src/RemoteRequest/StubbedRemoteGetRequest.php b/lib/common/src/RemoteRequest/StubbedRemoteGetRequest.php
index bd8fa8e7304..7fbebd52dee 100644
--- a/lib/common/src/RemoteRequest/StubbedRemoteGetRequest.php
+++ b/lib/common/src/RemoteRequest/StubbedRemoteGetRequest.php
@@ -2,7 +2,7 @@
 
 namespace AmpProject\RemoteRequest;
 
-use AmpProject\Exception\FailedToGetFromRemoteUrl;
+use AmpProject\Exception\FailedRemoteRequest;
 use AmpProject\RemoteGetRequest;
 use AmpProject\Response;
 use LogicException;
@@ -37,7 +37,7 @@ public function __construct($argumentMap)
      *
      * @param string $url URL to get.
      * @return Response Response for the executed request.
-     * @throws FailedToGetFromRemoteUrl If retrieving the contents from the URL failed.
+     * @throws FailedRemoteRequest If retrieving the contents from the URL failed.
      */
     public function get($url)
     {
diff --git a/src/RemoteRequest/CachedData.php b/src/RemoteRequest/CachedData.php
deleted file mode 100644
index df7ec8957dd..00000000000
--- a/src/RemoteRequest/CachedData.php
+++ /dev/null
@@ -1,71 +0,0 @@
-<?php
-/**
- * Class CachedData.
- *
- * @package AmpProject\AmpWP
- */
-
-namespace AmpProject\AmpWP\RemoteRequest;
-
-use DateTimeImmutable;
-use DateTimeInterface;
-
-/**
- * Serializable object that represents cached data together with its expiry time.
- *
- * @package AmpProject\AmpWP
- */
-final class CachedData {
-
-	/**
-	 * Cached value.
-	 *
-	 * @var mixed
-	 */
-	private $value;
-
-	/**
-	 * Expiry time of the cached value.
-	 *
-	 * @var DateTimeInterface
-	 */
-	private $expiry;
-
-	/**
-	 * Instantiate a CachedData object.
-	 *
-	 * @param mixed             $value Cached value.
-	 * @param DateTimeInterface $expiry Expiry of the cached value.
-	 */
-	public function __construct( $value, DateTimeInterface $expiry ) {
-		$this->value  = $value;
-		$this->expiry = $expiry;
-	}
-
-	/**
-	 * Get the cache value.
-	 *
-	 * @return mixed Cached value.
-	 */
-	public function get_value() {
-		return $this->value;
-	}
-
-	/**
-	 * Get the expiry of the cached value.
-	 *
-	 * @return DateTimeInterface Expiry of the cached value.
-	 */
-	public function get_expiry() {
-		return $this->expiry;
-	}
-
-	/**
-	 * Check whether the cached value is expired.
-	 *
-	 * @return bool Whether the cached value is expired.
-	 */
-	public function is_expired() {
-		return new DateTimeImmutable( 'now' ) > $this->expiry;
-	}
-}
diff --git a/src/RemoteRequest/CachedRemoteGetRequest.php b/src/RemoteRequest/CachedRemoteGetRequest.php
index 205caab11c3..fcf349a7899 100644
--- a/src/RemoteRequest/CachedRemoteGetRequest.php
+++ b/src/RemoteRequest/CachedRemoteGetRequest.php
@@ -7,6 +7,7 @@
 
 namespace AmpProject\AmpWP\RemoteRequest;
 
+use AmpProject\Exception\FailedToGetCachedResponse;
 use AmpProject\Exception\FailedToGetFromRemoteUrl;
 use AmpProject\RemoteGetRequest;
 use AmpProject\RemoteRequest\RemoteGetRequestResponse;
@@ -101,24 +102,23 @@ public function __construct(
 	 *
 	 * @param string $url URL to get.
 	 * @return Response Response for the executed request.
-	 * @throws FailedToGetFromRemoteUrl If retrieving the contents from the URL failed.
+	 * @throws FailedToGetCachedResponse If retrieving the contents from the URL failed.
 	 */
 	public function get( $url ) {
-		$cache_key   = self::TRANSIENT_PREFIX . md5( __CLASS__ . $url );
-		$cached_data = get_transient( $cache_key );
-		$headers     = [];
-		$status      = null;
+		$cache_key       = self::TRANSIENT_PREFIX . md5( __CLASS__ . $url );
+		$cached_response = get_transient( $cache_key );
+		$headers         = [];
 
-		if ( false !== $cached_data ) {
+		if ( false !== $cached_response ) {
 			if ( PHP_MAJOR_VERSION >= 7 ) {
-				$cached_data = unserialize( $cached_data, [ CachedData::class, DateTimeImmutable::class ] ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.serialize_unserialize,PHPCompatibility.FunctionUse.NewFunctionParameters.unserialize_optionsFound
+				$cached_response = unserialize( $cached_response, [ CachedResponse::class, DateTimeImmutable::class ] ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.serialize_unserialize,PHPCompatibility.FunctionUse.NewFunctionParameters.unserialize_optionsFound
 			} else {
 				// PHP 5.6 does not provide the second $options argument yet.
-				$cached_data = unserialize( $cached_data ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.serialize_unserialize
+				$cached_response = unserialize( $cached_response ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.serialize_unserialize
 			}
 		}
 
-		if ( false === $cached_data || $cached_data->is_expired() ) {
+		if ( ! $cached_response instanceof CachedResponse || $cached_response->is_expired() ) {
 			try {
 				$response = $this->remote_request->get( $url );
 				$status   = $response->getStatusCode();
@@ -131,12 +131,16 @@ public function get( $url ) {
 				$body   = $exception->getMessage();
 			}
 
-			$cached_data = new CachedData( $body, $expiry );
+			$cached_response = new CachedResponse( $body, $headers, $status, $expiry );
 
-			set_transient( $cache_key, serialize( $cached_data ) ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.serialize_serialize
+			set_transient( $cache_key, serialize( $cached_response ) ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.serialize_serialize
 		}
 
-		return new RemoteGetRequestResponse( $cached_data->get_value(), $headers, $status );
+		if ( ! $cached_response->is_valid() ) {
+			throw new FailedToGetCachedResponse( $url );
+		}
+
+		return new RemoteGetRequestResponse( $cached_response->get_body(), $cached_response->get_headers(), $cached_response->get_status_code() );
 	}
 
 	/**
diff --git a/src/RemoteRequest/CachedResponse.php b/src/RemoteRequest/CachedResponse.php
new file mode 100644
index 00000000000..194cfadd91a
--- /dev/null
+++ b/src/RemoteRequest/CachedResponse.php
@@ -0,0 +1,117 @@
+<?php
+/**
+ * Class CachedResponse.
+ *
+ * @package AmpProject\AmpWP
+ */
+
+namespace AmpProject\AmpWP\RemoteRequest;
+
+use DateTimeImmutable;
+use DateTimeInterface;
+
+/**
+ * Serializable object that represents a cached response together with its expiry time.
+ *
+ * @package AmpProject\AmpWP
+ */
+final class CachedResponse {
+
+	/**
+	 * Cached body.
+	 *
+	 * @var string
+	 */
+	private $body;
+
+	/**
+	 * Cached headers.
+	 *
+	 * @var array
+	 */
+	private $headers;
+
+	/**
+	 * Cached status code.
+	 *
+	 * @var int
+	 */
+	private $status_code;
+
+	/**
+	 * Expiry time of the cached value.
+	 *
+	 * @var DateTimeInterface
+	 */
+	private $expiry;
+
+	/**
+	 * Instantiate a CachedResponse object.
+	 *
+	 * @param string            $body         Cached body.
+	 * @param string[]          $headers      Associative array of cached headers.
+	 * @param int               $status_code  Cached status code.
+	 * @param DateTimeInterface $expiry       Expiry of the cached value.
+	 */
+	public function __construct( $body, $headers, $status_code, DateTimeInterface $expiry ) {
+		$this->body        = (string) $body;
+		$this->headers     = (array) $headers;
+		$this->status_code = (int) $status_code;
+		$this->expiry      = $expiry;
+	}
+
+	/**
+	 * Get the cached body.
+	 *
+	 * @return string Cached body.
+	 */
+	public function get_body() {
+		return $this->body;
+	}
+
+	/**
+	 * Get the cached headers.
+	 *
+	 * @return string[] Cached headers.
+	 */
+	public function get_headers() {
+		return $this->headers;
+	}
+
+	/**
+	 * Get the cached status code.
+	 *
+	 * @return int Cached status code.
+	 */
+	public function get_status_code() {
+		return $this->status_code;
+	}
+
+	/**
+	 * Determine the validity of the cached response.
+	 *
+	 * @return bool Whether the cached response is valid.
+	 */
+	public function is_valid() {
+		// Values are already typed, so we just control the status code for validity.
+		return $this->status_code > 100 && $this->status_code <= 599;
+	}
+
+	/**
+	 * Get the expiry of the cached value.
+	 *
+	 * @return DateTimeInterface Expiry of the cached value.
+	 */
+	public function get_expiry() {
+		return $this->expiry;
+	}
+
+	/**
+	 * Check whether the cached value is expired.
+	 *
+	 * @return bool Whether the cached value is expired.
+	 */
+	public function is_expired() {
+		return new DateTimeImmutable( 'now' ) > $this->expiry;
+	}
+}
diff --git a/tests/php/test-amp-style-sanitizer.php b/tests/php/test-amp-style-sanitizer.php
index be7a6ade443..7f912e32a10 100644
--- a/tests/php/test-amp-style-sanitizer.php
+++ b/tests/php/test-amp-style-sanitizer.php
@@ -7,7 +7,7 @@
 
 // phpcs:disable WordPress.Arrays.MultipleStatementAlignment.DoubleArrowNotAligned
 
-use AmpProject\AmpWP\RemoteRequest\CachedData;
+use AmpProject\AmpWP\RemoteRequest\CachedResponse;
 use AmpProject\AmpWP\RemoteRequest\CachedRemoteGetRequest;
 use AmpProject\AmpWP\Tests\AssertContainsCompatibility;
 use AmpProject\Dom\Document;
@@ -1587,22 +1587,24 @@ public function test_external_stylesheet_cache_control() {
 		$request_count = 0;
 		$href          = 'https://www.example.com/styles.css';
 		$response_body = 'body{color:red}';
+		$headers       = [
+			'content-type'  => 'text/css',
+			'cache-control' => 'max-age=' . ( YEAR_IN_SECONDS + MONTH_IN_SECONDS ),
+		];
+		$status_code   = 200;
 
 		add_filter(
 			'pre_http_request',
-			function( $preempt, $request, $url ) use ( $href, &$request_count, $response_body ) {
+			function( $preempt, $request, $url ) use ( $href, &$request_count, $response_body, $headers, $status_code ) {
 				$this->assertRegExp( '#^https?://#', $url );
 				if ( set_url_scheme( $url, 'https' ) === set_url_scheme( $href, 'https' ) ) {
 					$request_count++;
 					$preempt = [
 						'response' => [
-							'code'    => 200,
+							'code' => $status_code,
 						],
-						'headers' => [
-							'content-type' => 'text/css',
-							'cache-control' => 'max-age=' . ( YEAR_IN_SECONDS + MONTH_IN_SECONDS ),
-						],
-						'body' => $response_body,
+						'headers'  => $headers,
+						'body'     => $response_body,
 					];
 				}
 				return $preempt;
@@ -1645,16 +1647,18 @@ function( $preempt, $request, $url ) use ( $href, &$request_count, $response_bod
 		$this->assertNotFalse( $transient );
 
 		/**
-		 * Cached data.
+		 * Cached response.
 		 *
-		 * @var CachedData
+		 * @var CachedResponse
 		 */
-		$cached_data = unserialize( $transient ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.serialize_unserialize
-		$this->assertInstanceOf( CachedData::class, $cached_data );
+		$cached_response = unserialize( $transient ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.serialize_unserialize
+		$this->assertInstanceOf( CachedResponse::class, $cached_response );
 
-		$this->assertEquals( $response_body, $cached_data->get_value() );
+		$this->assertEquals( $response_body, $cached_response->get_body() );
+		$this->assertEquals( $headers, $cached_response->get_headers() );
+		$this->assertEquals( $status_code, $cached_response->get_status_code() );
 
-		$expiry = $cached_data->get_expiry();
+		$expiry = $cached_response->get_expiry();
 		$this->assertGreaterThan( ( new DateTimeImmutable( '+ 1 year' ) )->getTimestamp(), $expiry->getTimestamp() );
 
 		$sanitize_and_get_stylesheets();
@@ -1662,28 +1666,82 @@ function( $preempt, $request, $url ) use ( $href, &$request_count, $response_bod
 	}
 
 	/**
-	 * Test that external stylesheets fetches are cached when failures occur.
+	 * Data for test_external_stylesheet()
 	 *
+	 * @return array
+	 */
+	public function get_external_stylesheet_data() {
+		return [
+			'successful' => [
+				'style_url'     => 'https://www.example.com/styles.css',
+				'http_response' => [
+					'body'    => 'body { color: #fff }',
+					'code'    => 200,
+					'headers' => [
+						'cache-control' => 'max-age=1441',
+						'content-type'  => 'text/css',
+					],
+				],
+				'expected_styles' => [ 'body{color:#fff}' ],
+				'expected_errors' => [],
+				'cached_data'    => new CachedResponse(
+					'body { color: #fff }',
+					[
+						'cache-control' => 'max-age=1441',
+						'content-type'  => 'text/css',
+					],
+					200,
+					new DateTimeImmutable( '+ 1441 seconds' )
+				),
+			],
+			'failed' => [
+				'style_url'     => 'https://www.example.com/not-found/styles.css',
+				'http_response' => [
+					'body'    => 'Not Found!',
+					'code'    => 404,
+					'headers' => [
+						'content-type' => 'text/html',
+					],
+				],
+				'expected_styles' => [],
+				'expected_errors' => [ AMP_Style_Sanitizer::STYLESHEET_FETCH_ERROR ],
+				'cached_data'    => new CachedResponse(
+					FailedToGetFromRemoteUrl::withHttpStatus( 'https://www.example.com/not-found/styles.css', 404 )->getMessage(),
+					[],
+					404,
+					new DateTimeImmutable( '+ ' . DAY_IN_SECONDS . ' seconds' )
+				),
+			],
+		];
+	}
+
+	/**
+	 * Test that external stylesheets fetches are cached.
+	 *
+	 * @dataProvider get_external_stylesheet_data
 	 * @covers AMP_Style_Sanitizer::process_link_element()
+	 *
+	 * @param string         $style_url                Stylesheet URL.
+	 * @param array          $http_response            Mocked HTTP response.
+	 * @param array          $expected_styles          Expected minified stylesheets.
+	 * @param array          $expected_errors          Expected error codes.
+	 * @param CachedResponse $expected_cached_response Expected cache response.
 	 */
-	public function test_external_stylesheet_not_found() {
+	public function test_external_stylesheet( $style_url, $http_response, $expected_styles, $expected_errors, $expected_cached_response ) {
 		$request_count = 0;
-		$href          = 'https://www.example.com/styles.css';
 
 		add_filter(
 			'pre_http_request',
-			function( $preempt, $request, $url ) use ( $href, &$request_count ) {
+			function( $preempt, $request, $url ) use ( $style_url, $http_response, &$request_count ) {
 				$this->assertRegExp( '#^https?://#', $url );
-				if ( set_url_scheme( $url, 'https' ) === set_url_scheme( $href, 'https' ) ) {
+				if ( set_url_scheme( $url, 'https' ) === set_url_scheme( $style_url, 'https' ) ) {
 					$request_count++;
 					$preempt = [
 						'response' => [
-							'code'    => 404,
-						],
-						'headers' => [
-							'content-type' => 'text/html',
+							'code'    => $http_response['code'],
 						],
-						'body' => 'Not Found!',
+						'headers' => $http_response['headers'],
+						'body' => $http_response['body'],
 					];
 				}
 				return $preempt;
@@ -1692,8 +1750,8 @@ function( $preempt, $request, $url ) use ( $href, &$request_count ) {
 			3
 		);
 
-		$sanitize_and_get_stylesheets = static function() use ( $href ) {
-			$html = sprintf( '<html amp><head><meta charset="utf-8"><link rel="stylesheet" href="%s"></head><body></body></html>', esc_url( $href ) ); // phpcs:ignore WordPress.WP.EnqueuedResources.NonEnqueuedStylesheet
+		$sanitize_and_get_stylesheets = static function( $css_url ) {
+			$html = sprintf( '<html amp><head><meta charset="utf-8"><link rel="stylesheet" href="%s"></head><body></body></html>', esc_url( $css_url ) ); // phpcs:ignore WordPress.WP.EnqueuedResources.NonEnqueuedStylesheet
 			$dom  = Document::fromHtml( $html );
 
 			$found_error_codes = [];
@@ -1714,33 +1772,32 @@ function( $preempt, $request, $url ) use ( $href, &$request_count ) {
 
 		$this->assertEquals( 0, $request_count );
 
-		list( $found_error_codes, $actual_stylesheets ) = $sanitize_and_get_stylesheets();
+		list( $found_error_codes, $actual_stylesheets ) = $sanitize_and_get_stylesheets( $style_url );
 
-		$this->assertEquals( [ AMP_Style_Sanitizer::STYLESHEET_FETCH_ERROR ], $found_error_codes );
-		$this->assertEmpty( $actual_stylesheets );
+		$this->assertEquals( $expected_errors, $found_error_codes );
+		$this->assertEquals( $expected_styles, $actual_stylesheets );
 		$this->assertEquals( 1, $request_count, 'Expected HTTP request.' );
 
-		$cache_key = CachedRemoteGetRequest::TRANSIENT_PREFIX . md5( CachedRemoteGetRequest::class . $href );
+		$cache_key = CachedRemoteGetRequest::TRANSIENT_PREFIX . md5( CachedRemoteGetRequest::class . $style_url );
 		$transient = get_transient( $cache_key );
 		$this->assertNotFalse( $transient );
 
 		/**
-		 * Cached data.
+		 * Cached response.
 		 *
-		 * @var CachedData
+		 * @var CachedResponse
 		 */
-		$cached_data = unserialize( $transient ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.serialize_unserialize
-		$this->assertInstanceOf( CachedData::class, $cached_data );
+		$cached_response = unserialize( $transient ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.serialize_unserialize
+		$this->assertInstanceOf( CachedResponse::class, $cached_response );
 
-		$expected_exception = FailedToGetFromRemoteUrl::withHttpStatus( $href, 404 );
-		$this->assertEquals( $expected_exception->getMessage(), $cached_data->get_value() );
+		$this->assertEquals( $expected_cached_response->get_body(), $cached_response->get_body() );
+		$this->assertEquals( $expected_cached_response->get_headers(), $cached_response->get_headers() );
+		$this->assertEquals( $expected_cached_response->get_status_code(), $cached_response->get_status_code() );
 
-		// Verify that CachedRemoteGetRequest::$min_expiry is used for HTTP failures. It is set to 1 day.
-		$expiry = $cached_data->get_expiry();
-		$this->assertLessThanOrEqual( ( new DateTimeImmutable( '+ 1 day' ) )->getTimestamp(), $expiry->getTimestamp() );
-		$this->assertGreaterThan( ( new DateTimeImmutable( '+ 12 hours' ) )->getTimestamp(), $expiry->getTimestamp() );
+		$expiry = $cached_response->get_expiry();
+		$this->assertEquals( $cached_response->get_expiry()->getTimestamp(), $expiry->getTimestamp() );
 
-		$sanitize_and_get_stylesheets();
+		$sanitize_and_get_stylesheets( $style_url );
 		$this->assertEquals( 1, $request_count, 'Expected HTTP request to be cached.' );
 	}