In order to test a model we have to have some way of recognising the success or failure of a test, our test must have a goal, it must have a reason for existing.
That reason is inherent in the model from which the test is derived. This means that it is difficult to use a model to test itself. In software development this is typically not a problem, we rarely use the source code as the only model when testing the source code. We typically derive tests from a design model, a requirements model or a specific testing model, or even a model which may be derived from the source code, essentially any model which has the level of detail required for our testing.
Modelling is as fundamental an activity of testing as it is of development.
Test Strategies are applied to models. This is for the purposes of test derivation, derivation and execution coverage measurement, domain analysis, risk analysis, the list includes almost every task that testers do.
Strategies typically evolve and are identified by thinking about errors that slipped through and identifying a strategy that could have found them.