这个句子在英语里面有两种翻译方法,看你个人喜欢选择哪种翻译方式了。You will know who is the real friend when in trouble.
来个高级的、加上倒装: Not until you are in trouble will you know who is the real friend.
You will know who is the real friend when in trouble.
来个高级的、加上倒装: Not until you are in trouble will you know who is the real friend.
Only in trouble will you know who is your real friend.