be ready or forced to prove one's ability to cope well with a demanding situation奋发，鼓起勇气
put someone on their mettle
(of a demanding situation) test someone's ability to face difficulties（严峻形势）使奋发，激励某人战胜困难
on (one's) mettle
Prepared to accept a challenge and do one's best.奋发：准备接受挑战并尽最大努力
柯林斯高阶英汉双解学习词典释义
N-UNCOUNT
（应对困境的）勇气，才能，气魄
Someone's mettle is their ability to do something well in difficult circumstances.
例句
His first important chance to show his mettle came when he opened the new session of the Legislature...当他召开新一届立法会议的时候，让他展示才能的第一次重要机会来了。For both sides, it's the first real test of their mettle this season...对于双方而言，这是本赛季对他们的能力的首次真正考验。
PHRASE
鼓起勇气；全力以赴；振作精神
If you are on your mettle, you are ready to do something as well as you can, because you know that you are being tested or challenged.
例句
The added competition keeps them on their mettle.加赛让他们全力以赴。
英汉词典释义
n.
奋发起来；准备尽最大努力
When the boss comes round, I want you all to show your mettle.老板来的时候，我希望你们每个人都表现出自己最好的状态。He’ll have to be on his mettle if he wants to win the next race.他如果想赢得下次比赛，就得全力以赴。
使某人尽最大努力；充分发掘某人的潜质
The school inspection is going to put the teachers on their mettle.对学校的视察将使教师发挥出他们的全部潜力。
英英词典释义
Noun
1. the courage to carry on;
"he kept fighting on pure spunk""you haven't got the heart for baseball"