They may not be the market-cleansing mechanism most hope for, he says in an essay in the FT. His conclusion:

European officials can do a lot to make the stress test credible; and they should. But, unfortunately, they cannot turn it into a catalyst for Europe’s return to financial normality. Regrettably, this is a much bigger challenge. It was long in the making and will require a more comprehensive solution whose implementation is inherently more complex and protracted.