  Computational theory and practice generally focus on single-paradigm systems,
but relatively little is known about how best to combine components based on
radically different approaches (e.g., silicon chips and wetware) into a single
coherent system. In particular, while testing strategies for single-technology
components are generally well developed, it is unclear at present how to
perform integration testing on heterotic systems: can we develop a test-set
generation strategy for checking whether specified behaviours emerge (and
unwanted behaviours do not) when components based on radically different
technologies are combined within a single system?
  In this paper, we describe an approach to modelling multi-technology
heterotic systems using a general-purpose formal specification strategy based
on Eilenberg's X-machine model of computation. We show how this approach can be
used to represent disparate technologies within a single framework, and propose
a strategy for using these formal models for automatic heterotic test-set
generation. We illustrate our approach by showing how to derive a test set for
a heterotic system combining an X-machine-based device with a cell-based P
system (membrane system).
