If someone answers testily, they answer in a short, impatient, slightly bad-tempered way — the tone of a person whose patience has just run out. It is not shouting or real anger; it is the sharp edge in the voice of someone who is tired, or who has been asked the same thing three times. You meet it most in novels and news writing, almost always beside a speaking verb: he said testily, she replied testily, 'What now?' he asked testily. In everyday spoken English people would say crossly, sharply, or 'in an irritated voice' instead. So treat it as a reading word more than a speaking word: recognising it tells you a lot about how a character in a story is feeling.

沒好氣地、不耐煩地（回話）。多用在小說敘述裡，口語比較少講。