Exchanges passed two recent tests of their ability to handle an explosion of trading. They face a third and potentially greater challenge today, when the Federal Reserve decides whether to raise interest rates for the first time in nine years.

On Aug. 24, as anxiety engulfed markets worldwide and prompted one of the worst days for stocks since the aftermath of the 2008 financial crisis, no exchanges reported malfunctions. U.S. stock exchanges weathered a surge in volume to a four-year high of 14.1 billion shares. Last year, a wild session for Treasuries and other assets prompted no obvious malfunctions on Oct. 15, when 11.9 billion U.S. shares traded.

Technical errors at prominent financial markets in recent years have eroded public confidence and prompted regulators to demand they do better. With the Fed's decision likely to unleash another tsunami of volume, exchanges face another big test.