Windowed comparison for differences in the middle of long strings

[cohuman]

When two strings fail to match, if the difference is somewhere in the middle of the strings, it can be annoying/impossible to track down the actual difference. I've written a little Comparison object that provides this kind of error message:

Strings differ at position 12:
expected: ..."efghijklmnopqrst"...
actual: ..."efghijklXnopqrst"...

It shows a "prelude" of a few characters, then the difference, on successive lines so they're easy to visually scan. It also does the right thing (or tries to) if the difference is near the beginning or end of the string (i.e. does or doesn't show ellipses).

http://gist.github.com/474363

For people who can't wait for this to get incorporated into RSpec proper, you can require comparison.rb and it'll override the existing RSpec == matcher.

One open question is whether the exception message should show the full actual string as well as the comparison... On one hand, it adds to screen clutter, but on the other hand, it can be important in tracking down the problem, especially if the prelude is ambiguous.

[dchelimsky]

Hey Alex,

Do you think this is best served as part of rspec proper, or as an extension? My instinct is to have it be an extension so that folks could use it with test/unit and/or minitest as well. WDYT?

[myronmarston]

I'm with @dchelimsky here -- I'm not sure this belongs in rspec, but it does sound useful.

Given that this has sat for 2 years with no one else piping in, I'm going to close this as a stale ticket.