The overall aim is to force banks into a position where they would need to dig into their capital reserves and add risk to their balance sheets. The test intentionally contracts the markets primary supply of liqudity with a $25 billion reduction in QE spending, meaning that the gap would have to be compensated for by the financial sector. Then the FED sells some its risk back onto the market to raise short term interest rates, which will expose the real strength of the banking sector, as interbank loan interest would increase in relation to Federal Funds. Markets alongside the FED would be able to assess the cash positions and capital reserves of the nation's banks, as institutions with ample reserves in cash will be able to take on more risk through lending, and also will be able to borrow at lower interest rates. Banks unable or unwilling to cope with higher rates would be discovered and the central bank would have a clearer idea of where to lend, rather than filtering capital through the entire banking system.
Given Bernanke's committment to accomodative policy until America makes significant headway on unemployment and growth, it's unlikely the Federal Reserve would pursue this course. However, QE's power to catalyze growth throughout the broader economy wanes with each use, as firms prefer to simply garrison the cash rather than invest it through job creation and hiring. With Congress embroiled in the debate over tax and entitlement reform, fiscal policy to address this problem isn't likely to arrive anytime soon. This problem falls to the FED to resolve, and something has to give.