Not vulnerable versus vulnerable at matchpoints, I opened with a pass, LHO bid one spade, and partner bid two spades (Michaels), showing 5-5 in hearts and a minor.
I bid three diamonds with the following hand (because my hearts were not long or strong enough to bid): ♠ 854 ♡Q8 ♢A6542 ♣ T94.
I "lucked out" because partner had JT987 of diamonds and a singleton club. We would have suffered if her minor suits had been reversed.
One of the opponents pointed out that my diamond holding wasn't strong enough to make a unilateral decision (I should have bid 2NT to let partner indicate the suit).
If I had it to do again, I would bid 2NT with my actual diamond holding, but I would bid 3 diamonds with AKxxx. Is this suit strong enough to bid diamonds unilaterally when I have three clubs? Suppose my minor suit holdings were ♢AK654 and ♣4? (In this case, I would have had only one club, if her suit were clubs, and my five diamonds would be decidedly stronger than her "average expectations" of KJxxx.)