Regarding the tests, I don't see tests for the aliases anywhere, so something like:
for alias, codec_name in encodings.aliases.items():
   self.assertEqual(codecs.lookup(alias).name, codec_name)
could be added somewhere to check that all the aliases in the dict map to the correct codec.

Well, actually encodings.aliases links to the encoding _module name_, as described in the doc:
""" Encoding Aliases Support
    This module is used by the encodings package search function to
    map encodings names to module names.
"""
So I've adjusted your snippet according to this, as you can see in the attachment.

I've also slightly changed the imports as pep8 says:
"""
Yes: import os
import sys

No: import sys, os