We usually model subsets of features that are
about the right size for a tester??™s work assignment (a typical test suite). We usually
choose a level of abstraction where actions in the model correspond to actions in the
implementation that are easy to observe and instrument (such as calls to methods in
its API).
Moreover, we believe that the tester??™s point of view is especially helpful in keeping
the models grounded in reality. In order to perform conformance testing, which
involves lockstep execution of the model with the implementation, the tester must
write a test harness that couples the implementation to the model through the test
Overview 11
tool. This test harness makes the correspondence between the model and the implementation
completely explicit. Writing this harness, and the subsequent lockstep
execution itself, closes the loop from the model back to the implementation. It validates
the model with a degree of thoroughness that is not easily achieved in projects
that do not use the models for testing.
1.5 Syllabus
This book teaches how to write and analyze model programs, and how to use them
to test implementations. Here is a brief summary of the topics to come.
The book is divided into four parts. The end of each part is an exit point; a reader
who stops there will have coherent understanding and tools for modeling, analysis,
and testing up to that level of complexity.
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