2 Why We Need Model-Based Testing

322 Glossary
implementation under test (IUT). The implementation that is the subject of testing,
that is executed during test runs.
indexer. In C#, a construct that accesses a data structure using indices, as if it were
an array. The NModel library provides access to the arguments of an action term
through an indexer.
“infinite.” Perhaps not mathematically infinite, but too large to store each element,
or to consider each element one by one. Exhaustive analysis of an “infinite” program
is not feasible; the analysis must be finitized.
infinitely branching. Amodel program where an “infinite” number of transitions
are enabled in some states, because actions have “infinite” domains. An infinitely
branching model program is not explorable, but can be made explorable by appropriate
parameter generation.
informal. Expressed in a notation that cannot be analyzed automatically, such as
natural language or hand-drawn diagrams. Contrast to formal.
initial state. The state where a run begins. It is necessary to identify the initial state
of an FSM.
inspection.Anassurance method where people examine documents or code, checking
for errors. Informal documents can be inspected.
interesting.Astate that is partially explored or that has a path leading to a partially
explored state. A strategy might give priority to actions that lead to interesting states.
internal action. An action in a model program that has no corresponding action in
the implementation and is not executed by the stepper. Internal actions are typically
used to select among test cases in a test suite.
intersection. Aset that contains the elements shared by two sets. Or, the operation
on two sets that returns their intersection. In composition, the allowed traces of
the product belong to the intersection of the traces of the loop extensions of the
individual model programs.
invariant. Apredicate that is supposed to be true in every state that is reachable.
Invariants express safety requirements.
invocation. A method call, including the method name and all of its arguments. Or,
the execution of that method call. The invocation of an action method is an action.
isomorphic states. States where there exists a substitution of abstract values that
makes them equal. Isomorphic means “same shape.” For example, states are isomorphic
if they store data structures which have the same shape and store the same
values, except for object IDs. Excluding isomorphic states can greatly reduce the
number of states that must be considered during exploration.
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