[rspec-users] rspec runner setting $KCODE considered harmful?

David Chelimsky dchelimsky at gmail.com
Thu Sep 23 09:44:49 EDT 2010

On Sep 22, 2010, at 9:47 PM, Josh Whiting wrote:

> I ran across a problem today in which some code ran fine in regular operation but failed in a test case. I scratched my head and thought "why would running from within the test harness change the behavior of my code?" Clearly it was the Heisenberg uncertainty principle in action! :)
> I discovered the root cause was that the rspec runner is setting the magical ruby global, $KCODE, to 'u'. However, my application (which is not a rails app) had never specified $KCODE. I was relying on some default behavior of regular expressions under ruby 1.8 (byte-wise character matching semantics) that *change* when $KCODE is set to "u". Specifically, all regular expressions change their default behavior to utf-8 character-wise semantics. A simple example of this phenomenon: http://gist.github.com/592990
> I've corrected the issue on my end by adopting the $KCODE='u' semantics in my application, but this led me to a couple comments/questions I thought would be relevant to raise with other rspec-minded folks:
> - Is it necessary for rspec to set $KCODE or is this a bug?Wouldn't it be better if it didn't twiddle any magical globals that change interpreter-wide behaviors? It reminds me of the bad days of perl when some distant code would unexpectedly change out your line terminator character on you.
> - It seems like a good idea to call out all the things the rspec environment changes that affect natural runtime behavior of code: twiddling of globals, class monkey patches, etc. It'd be great to get these into a list of publicly documented pitfalls for people to watch out for.
> Thanks for listening. Rspec has brought huge value to my engineering project and I really appreciate the tool!

I don't remember the details, but that was added to solve a particular problem back in 2005 or 2006. Changing it in RSpec-1 would break some existing specs with a minor upgrade, so that's a non-option.

This does not get set, however, in RSpec-2. I added a note about this to http://github.com/rspec/rspec-core/blob/master/Upgrade.markdown

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