organic chemistry - Why do α-hydroxy ketones give Tollens' test?

I know that tautomerism causes the $\alpha$-hydroxy ketones to give the all the tests of an aldehyde. But how does it exactly tautomerise and what's the intermediate?

Does benzoin gives Tollens' test? If not, why? I'm really confused with this. I read somewhere that benzoin doesn't give Tollens' test as it does not have an alpha carbon to form enediol intermediate. Please help.