This is aHand:

Sometimes covering an honor with an honor promotes a trick in your hand or in your partner's.

Sometimes it throws away a trick that would have gone your way if you had the patience to wait for it.

Which of those occasions is this? Or, more accurately, are these?

You lead the ♦10 against 4♥ by East; declarer wins trick one with the ♦Q then leads the ♥Q. Should you cover that honor with the ♥K?

The answer is a firm No. You do not cover because you have more Hearts than dummy and if you play low on each round of trumps your ♥K cannot be caught. Anyway, there is nothing to promote (partner can't have anything in Hearts).

Declarer continues with the ♥J then, noting the 4-1 trump break, switches to a Club playing the ♣Q from dummy. Your partner (North) wins with the ♣A and plays  back the ♣J, putting declarer back on table with the ♣K.

Declarer comes to hand with a Diamond and tries his luck with the â™ J. This is test number two. Do you cover that honor with your honor?

The answer again is No. Although you cannot see what is in declarer's hand you can be sure that East has either the ♠Q J or the ♠J 10 and in neither case would it be right to cover touching honors.

The ♠J runs to the ♠Q and North plays another Club, ruffed and overruffed by your ♥K. You exit with yet another Diamond. Declarer can now draw the last trump and lead the ♠10. Do you cover that?

This time the answer is a resounding Yes. If you don't cover then you can see that the ♠10 will be run and declarer will have the rest. So it is no-cost to cover with the ♠K. As the cards lie this promotes partner's ♠9 as the setting trick.

Phew! It's easy to go wrong on this testing deal.