def format_error(e)
      format = ["    #{e.class.name} occurred", "#{e.to_s}"]
      filter_backtrace(e.backtrace) { |line| format << "      at #{line}" }
      format.join("\n")
    end
Generates a message for assertions that error out. However, in the additional stacktrace, any mentions
of Riot and Rake framework methods calls are removed. Makes for a more readable error response.

@param [Exception] e the exception to generate the backtrace from
@return [String] the error response message