It would be nice to be able to assert that a response is indeed a PDF. Right now, I'm doing it with something like: ```php $I->seeHttpHeader('Content-Type', 'application/pdf'); $I->seeResponseContains('%PDF-1.'); ``` REST module has [`seeResponseIsJson()`](https://codeception.com/docs/modules/REST#seeResponseIsJson) and [`seeResponseIsXml()`](https://codeception.com/docs/modules/REST#seeResponseIsXml)