module Minitest::Assertions

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