is there a way to test binary data ?

superagent has responseType, however it seems that method is not exposed by supertest ?
```
request(app).get('/sub/asset1.a').responseType('blob')
```
yields
```
responseType is not a function
```

Start at the SuperTest request API around request(app).get(...) and compare its exposed methods with SuperAgent's responseType. Done means binary data can be requested through the documented API and a test covers the behavior.

Written by the indexing model from the issue text.