Agent-based modeling and simulation (ABMS) became an attractive and efficient way to model large-scale complex systems. The use of models always raises the question whether the model is correctly encoded (verification) and accurately represents the real system (validation). However, achieving a sufficiently credible agent-based simulation (ABS) model is still difficult due to weak verification, validation and testing (VV&T) techniques. Moreover, there is no comprehensive and integrated toolkit for VV&T of ABS models that demonstrates that inaccuracies exist and/or which reveals the existing errors in the model. Based on this observation, we designed and developed RatKit: a toolkit for ABS models to conduct VV&T. RatKit facilitates the VV&T process of ABMS by providing an integrated environment that allows repeatable and automated execution of ABS tests. This paper presents RatKit in detail and demonstrates its effectiveness by showing its applicability on a simple well-known case study: predator - prey.