Case-sensitive uniqueness validation fails if default value lacks alpha characters

[tovodeverett]

I've run into a fairly unique situation, but I thought I'd bring it up in case someone wants to defend against it.

If your factory for generating objects uses a string that does not have change with swapcase (i.e. something like '%-1-%'), and you're doing a validate_uniqueness_of test without specifying case_insensitive, then you will get a rather confusing error message.

Perhaps it might make sense somewhere around https://github.com/thoughtbot/shoulda-matchers/blob/master/lib/shoulda/matchers/active_record/validate_uniqueness_of_matcher.rb#L410 to check to see that the swapcased value differs from the original value and if it doesn't to throw an error along the lines of, "if you're not doing a case_insensitive test, then you need to make sure your value here has alpha characters in it!".

[mcmire]

Moving discussion to #789.