public function testException()
 {
     $exception = new \Exception("Error Processing Request");
     $response = $this->execute([Middleware::ErrorHandler()->handler(function ($request, $response) {
         $exception = $request->getAttribute('EXCEPTION');
         $response->getBody()->write((string) $exception);
     })->catchExceptions(), function ($request, $response, $next) use($exception) {
         throw $exception;
     }]);
     $this->assertEquals(500, $response->getStatusCode());
     $this->assertEquals((string) $exception, (string) $response->getBody());
 }