Europe’s biggest banks are facing a day of judgment as the European Central Bank prepares to unveil the results of a yearlong search through the dark corners of their finances. It’s a step that comes none too soon for the struggling economy of the 18-country eurozone. The ECB review to be unveiled Sunday seeks to identify banks that are too weak to lend to businesses or make it through another recession and force them to strengthen their finances. It includes a detailed look at 130 banks’ loans, holdings and investments, as well as a so-called stress test that simulates how...