# File lib/active_support/core_ext/hash/keys.rb, line 14
        def stringify_keys!
          keys.each do |key|
            unless key.class.to_s == "String" # weird hack to make the tests run when string_ext_test.rb is also running
              self[key.to_s] = self[key]
              delete(key)
            end
          end
          self
        end