public function testPsrHttpResponse()
 {
     $signature = new Burthorpe\Runescape\Signature\Signature('iWader');
     $response = $signature->psrHttpResponse();
     $this->assertInstanceOf(\GuzzleHttp\Psr7\Response::class, $response);
     $this->assertSame(200, $response->getStatusCode());
     $this->assertSame([0 => 'image/png'], $response->getHeader('Content-Type'));
 }