The Silver test has two definitions:
1) A heuristic used to evaluate low-cost kingdom cards: a Silver would.or card is only worth buying if it will benefit the deck more than buying
2) The idea that Dominion is a solved game that only requires one to buy Treasure cards to win.
In the first sense, it's in fact very valuable to consider the relative value of kingdom cards to Silver, both in general, and at one's current point in a game. Being able to recognize this relative value is one of the keys to becoming a better Dominion player. However, it is the second sense that "Silver test" most often refers to.
In 2009, the BoardGameGeek user Stormparkiet posted Why Dominion did not deliver for me, in which they put forward that the whole point of Dominion is to get lots of Silvers in hand in order to buy Provinces, and that players should only buy cards that facilitate this specific action. Theory, founder of DominionStrategy, famously refuted this idea in his influential article Beyond Silver.