Now I feel this like should be:
```ruby
assert_equal Encoding::UTF_8, URL.unescape_path("/rails%E7%AC%94%E8%AE%B0/2014/04/20/escaped/".encode(Encoding::ASCII)).encoding
```

As in the test that string will always be `utf-8`, or at least that's what I think. But I'm not sure tho.