Misfortune tests the sincerity of friendship.

Adversity tests the sincerity of friends

Misfortune shows those who are not really friends.

Prosperity makes friends, adversity tries them.

Friends disappear
or they are powerless.
This is what misfortune means
an acid test of friendship.
I wouldn't wish it on anyone.

Unfortunate is he who cannot gain a few sincere friends during his life and more unfortunate is the one who has gained them and then lost them (through his deeds).

Sometimes the cost of integrity is the loss of a friend.

Misfortune comes uninvited

Friends show their love in times of trouble, not in happiness.

According as men thrive, their friends are true; if their affairs go to wreck, their friends sink with them. Fortune finds friends.

When our friends have deceived us we owe them but indifference to the tokens of their friendship, yet for their misfortunes we always owe them pity.

The real test of friendship and solidarity is not where one stands when the weather is fair and the sun is shining but rather where one stands at a time of storm and stress.

Translation: Doubtful circumstances disclose undoubted friends.

A foolish friend may cause more woe
Than could, indeed, the wisest foe.