diff --git a/app/tests/Handler/AsyncHandlerTest.php b/app/tests/Handler/AsyncHandlerTest.php
index 3280b9b..1038afe 100644
--- a/app/tests/Handler/AsyncHandlerTest.php
+++ b/app/tests/Handler/AsyncHandlerTest.php
@@ -30,10 +30,12 @@ class AsyncHandlerTest extends TestCase
         $response = $app->handle($request);
 
         $this->assertStringContainsString('<li>1</li>', $response->getBody());
+        $this->assertEquals("text/html", $response->getHeader('Content-Type')[0]);
 
         $request = $this->createRequest('GET', '/test', [ 'Accept' => 'application/json']);
         $response = $app->handle($request);
 
         $this->assertEquals('{"list":[1,2,3]}', $response->getBody());
+        $this->assertEquals("application/json", $response->getHeader('Content-Type')[0]);
     }
 }