# File lib/minitest/unit.rb, line 317
    def assert_output stdout = nil, stderr = nil
      out, err = capture_io do
        yield
      end

      err_msg = Regexp === stderr ? :assert_match : :assert_equal if stderr
      out_msg = Regexp === stdout ? :assert_match : :assert_equal if stdout

      y = send err_msg, stderr, err, "In stderr" if err_msg
      x = send out_msg, stdout, out, "In stdout" if out_msg

      (!stdout || x) && (!stderr || y)
    end