Domain-specific modelling languages (DSML) enable domain users to model systems in their problem domain, using concepts and notations they are familiar with. The process of domain-specific modelling (DSM) consists of two stages: A language engineering stage where a DSML is created, and a system modelling stage where the DSML is used. Because techniques such as metamodelling and model transformation allow for an efficient creation of DSMLs, and using DSMLs significantly increases productivity, DSM is very suitable for early prototyping. Many systems that are modelled using DSMLs are reactive, meaning that during their execution, they respond to external input. Because of the complexity of input and response behaviour of reactive systems, it is desirable to test models as early as possible. However, while dedicated testing support for specific DSMLs has been provided, no systematic support exists for testing DSML models according to DSM principles. In this paper, we introduce a technique to automatically generate a domain-specific testing framework from an annotated DSML definition. In our approach, the DSML definition consists of a metamodel, a concrete syntax definition and operational semantics described as a schedule of graph rewrite rules, thus covering a large class of DSMLs. Currently, DSMLs with deterministic behaviour are supported, but we provide an outlook to other (nondeterministic, real-Time or continuous-Time) DSMLs. We illustrate the approach with a DSML for describing an elevator controller. We evaluate the approach and conclude that compared to the state-ofthe-Art, our testing support is significantly less costly, and similar or better (according to DSM principles) testing support is achieved. Additionally, the generative nature of the approach makes testing support for DSMLs less error-prone while catering the need for early testing.