We might want to update the test so that it loads the generated serialization and makes sure it is valid and equal to `key`.

We can not use 

```
result_key = Key.fromFile()
```

since it requires a filename and we only have in memory files.

We can use `result_key = Key.fromString(public_key_file_serialization)` as we already tested that this is what is stored in the file... so we don't need to read it again.

The API for Key is here http://twistedmatrix.com/documents/12.0.0/api/twisted.conch.ssh.keys.Key.html

the test might look like

```
self.assertEqual(key.data, result_key.data)
```