2 Why We Need Model-Based Testing

326 Glossary
protocol. An agreement about how two or more agents work together. A protocol
is defined by rules for forming messages and rules that constrain the ordering of the
messages. When modeling a protocol, the messages are actions.
pruning. To limit exploration by systematically excluding some transitions. Examples
of pruning techniques include state filters, strengthening enabling conditions,
state groupings, and stopping rules. Pruning is a way to finitize. Contrast to
sampling.
pure. A statement or expression that has no side effects. Anenabling condition or
any other predicate must be pure.
random. A simple strategy that randomly selects an enabled action to execute next.
reachable. Ofastate, that it is visited by some possible run. A reachable state
might be visited during exploration. Of an object, that it occurs within a global state
variable, or occurs within an instance field of a reachable object. The keys of a field
map contain all reachable instances of its class.
reactive system. A system that responds to its environment. In a reactive system,
some of the actions are observable. Contrast to closed system.
reference equality. Where two variables are equal when occupy the same location
in memory. In C#, the default equality for objects. Contrast to structural equality.
restricted model.Ascenario model program created by restricting a contract model
program, especially by limiting domains.
review. Inspection.
reward. A quantity that a strategy seeks to maximize, by choosing the best action
in each state.
run. A sequence of actions. A run begins in the initial state and should stop in an
accepting state; otherwise, it is considered a liveness failure.
run-time check. To execute an assertion to check that the program or its environment
is behaving as intended.
safety. The property that nothing bad will happen: execution will not reach any unsafe
states that violate safety requirements. Or, no unsafe scenarios will be executed.
Contrast to liveness.
safety analysis. Checking safety, by searching for unsafe states or attempting to
execute a scenario.
safety requirement. Invariant.
sampling. To limit exploration by selecting desirable paths to explore, rather than
excluding undesirable transitions as with pruning. Sampling is a way to finitize.
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