2 Why We Need Model-Based Testing

Systems with Complex State 173
Client state
Clients of the revision control system have several elements of state. Since these
occur on a per-client basis, we can use maps whose keys are client names.
partial static class User
{
static Map version
= Map.EmptyMap;
}
static Map revisions
= Map.EmptyMap;
static Map conflicts
= Map.EmptyMap;
static Set commitPending = Set.EmptySet;
The version state variable records the version of the global repository that corresponds
with the most recent commit operation. This is a per-client element of state
because clients may synchronize with the global repository at different times. The
ability of clients to take a snapshot of the repository’s state is an important feature
of the revision conrol system.
The revisions state variable records for each client which files contain pending
edits for that client. The value is a map of file names to the current edit operation.
The conflicts state variable is used when committing changes to the database.
It contains a set of files with version conflicts. Such files must be resolved before a
change may be committed to the repository.
The commitPending state variable records whether a client is in the process
of perfoming a commit operation. Client operations are disabled when there is a
pending commit operation.
Derived state
The C# model program includes several elements of derived state. These are methods
or properties that query the state but do not change it.
partial static class User
{
static bool CommitPending(string user)
{ return commitPending.Contains(user); }
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