While value-at-risk has been the standard risk measure for a long time, expected shortfall (ES) has become more and more popular in recent times, as it provides important information about tail risk. We present a new backtest for the unconditional coverage property of the ES. The test is based on the so-called cumulative violation process, and its main advantage is that the distribution is known for finite out-of-sample size. This leads to better size and power properties compared with existing tests. Moreover, we extend the test principle to a multivariate test and analyze its behavior via simulations and an application to bank returns.