Remarks on Testing Probabilistic Processes Yuxin Deng, Rob van Glabbeek, Matthew Hennessy, Carroll Morgan, and Chenyi Zhang We develop a general testing scenario for probabilistic processes, giving rise to two theories: \emph{probabilistic may testing} and \emph{probabilistic must testing}. These are applied to a simple probabilistic version of the process calculus CSP. We examine the algebraic theory of probabilistic testing, and show that many of the axioms of standard testing are no longer valid in our probabilistic setting; even for non-probabilistic CSP processes, the distinguishing power of probabilistic tests is much greater than that of standard tests. We develop a method for deriving inequations valid in probabilistic may testing based on a probabilistic extension of the notion of \emph{simulation}. Using this, we obtain a complete axiomatisation for non-probabilistic processes subject to probabilistic may testing.