MiniTest failing on IO#external_encoding call

[mmmries]

I tried using minitest with a little puma + sinatra example app and Minitest fails while trying to show failure outputs. I get something like this:

Finished in 0.353042s, 28.3252 runs/s, 0.0000 assertions/s.
during at_exit handler 1: error , NoMethodError: undefined method `external_encoding' for File
a RubySystemExit occurred (error 2752)
topaz 1> exit

It looks to be related to this line in minitest and the method is documented here as part of the ruby 1.9.3 docs.

[zenspider]

Why is this true in maglev?

ENCS = "".respond_to? :encoding

[timfel]

There was a push to add encoding support, and we thought we had most things stubbed out so the basics (utf8, binary, ascii) work. I would say we missed adding support on files