Simulation can be an important conceptual and practical tool to support the engineering of multi-agent systems (MAS), in different ways-testing in particular. In this paper we consider the case in which simulation is applied and exploited directly upon a MAS developed using an existing agent programming/-MAS programming platform. That is: without requiring to model and simulate agents and their environment using a different platform (e.g., an agent-based simulation one). In particular, we describe the design and prototype implementation of JaCaMo-sim, an extension of the JaCaMo platform that makes it possible to both run and simulate the execution of MAS programs based on BDI agents written in Jason, situated in artifact-based environments developed in CArtAgO. The tool can be useful for different aspects that concern MAS engineering, from MAS testing at development time to-in perspective-agent decision making support at runtime.