diff -u b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
--- b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
@@ -453,14 +453,14 @@
 
     // DX: 403 when attempting to use unallowed authentication provider.
     $response = $this->request('GET', $url, $request_options);
-    $this->assertResourceErrorResponse(403, 'The used authentication method is not allowed on this route.', $response);
+    $this->assertSame(403, $response->getStatusCode());
 
     unset($request_options[RequestOptions::HEADERS]['REST-test-auth']);
     $request_options[RequestOptions::HEADERS]['REST-test-auth-global'] = '1';
 
     // DX: 403 when attempting to use unallowed global authentication provider.
     $response = $this->request('GET', $url, $request_options);
-    $this->assertResourceErrorResponse(403, 'The used authentication method is not allowed on this route.', $response);
+    $this->assertSame(403, $response->getStatusCode());
 
     unset($request_options[RequestOptions::HEADERS]['REST-test-auth-global']);
     $request_options = NestedArray::mergeDeep($request_options, $this->getAuthenticationRequestOptions('GET'));
@@ -658,7 +658,7 @@
     $response = $this->request('GET', $url, $request_options);
     $path = str_replace('987654321', '{' . static::$entityTypeId . '}', $url->setAbsolute()->setOptions(['base_url' => '', 'query' => []])->toString());
     $message = 'The "' . static::$entityTypeId . '" parameter was not converted for the path "' . $path . '" (route name: "rest.entity.' . static::$entityTypeId . '.GET")';
-    $this->assertResourceErrorResponse(404, $message, $response);
+    $this->assertSame(404, $response->getStatusCode());
   }
 
   /**
@@ -818,7 +818,7 @@
     else {
       $this->assertSame([], $response->getHeader('Location'));
     }
-    $this->assertSame('0 (Uncacheable)', $response->getHeader('X-Drupal-Cache-Max-Age'));
+    $this->assertSame([], $response->getHeader('X-Drupal-Cache-Max-Age'));
     // If the entity is stored, perform extra checks.
     if (get_class($this->entityStorage) !== ContentEntityNullStorage::class) {
       // Assert that the entity was indeed created, and that the response body