Why does Benzoin give positive Tollen's Test?
For benzoin, a similar mechanism of tautomerisation (of alpha hydroxy ketones tautomerising to aldehydes) happens , except for one step, where instead of the hydride ion (H-) migrating to the sp2 hydridized carbon, it is the Benzene carbanion (C6H5- or Ph-) that migrates to the sp2 hybridized carbon, since it is more stable than the hydride ion (an example of the stability of benzene carbanion over the hydride ion can be found in the pinacol-pinacalone rearrangement). Other than that, the rest of the mechanism is exactly the same.

Hope this cleared your doubt.