# File lib/test/unit/assertions.rb, line 767
        def extract_tag
          tag = nil
          if @@have_uncaught_throw_error
            return nil unless @error.is_a?(UncaughtThrowError)
            tag = @error.tag
          else
            pattern = UncaughtThrowPatterns[@error.class]
            return nil if pattern.nil?
            return nil unless pattern =~ @error.message
            tag = $1
          end
          normalize_tag(tag)
        end