--- /dev/null
+<?php
+
+namespace Drupal\Tests\serialization\Unit\EventSubscriber;
+
+use Drupal\serialization\Encoder\JsonEncoder;
+use Drupal\serialization\EventSubscriber\DefaultExceptionSubscriber;
+use Drupal\Tests\UnitTestCase;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpFoundation\Response;
+use Symfony\Component\HttpKernel\Event\GetResponseForExceptionEvent;
+use Symfony\Component\HttpKernel\Exception\MethodNotAllowedHttpException;
+use Symfony\Component\HttpKernel\HttpKernelInterface;
+use Symfony\Component\Serializer\Serializer;
+
+/**
+ * @coversDefaultClass \Drupal\serialization\EventSubscriber\DefaultExceptionSubscriber
+ * @group serialization
+ */
+class DefaultExceptionSubscriberTest extends UnitTestCase {
+
+ /**
+ * @covers ::on4xx
+ */
+ public function testOn4xx() {
+ $kernel = $this->prophesize(HttpKernelInterface::class);
+ $request = Request::create('/test');
+ $request->setRequestFormat('json');
+
+ $e = new MethodNotAllowedHttpException(['POST', 'PUT'], 'test message');
+ $event = new GetResponseForExceptionEvent($kernel->reveal(), $request, 'GET', $e);
+ $subscriber = new DefaultExceptionSubscriber(new Serializer([], [new JsonEncoder()]), []);
+ $subscriber->on4xx($event);
+ $response = $event->getResponse();
+
+ $this->assertInstanceOf(Response::class, $response);
+ $this->assertEquals('{"message":"test message"}', $response->getContent());
+ $this->assertEquals(405, $response->getStatusCode());
+ $this->assertEquals('POST, PUT', $response->headers->get('Allow'));
+ $this->assertEquals('application/json', $response->headers->get('Content-Type'));
+ }
+
+}