2 Why We Need Model-Based Testing

Systems with Complex State 193
This test run executes:
TestResult(0, Verdict("Success"), "",
Trace(
ServerSocket(),
ServerBind(),
ServerListen(),
ClientSocket(),
ClientConnect(),
ServerAccept(),
ServerSend(double("99.9")),
ClientReceive_Start(),
ClientReceive_Finish(double("99.9")),
ServerSend(double("99.9")),
ClientReceive_Start(),
ClientReceive_Finish(double("99.9")),
ClientSend(),
ServerReceive(),
ServerSend(double("100")),
ClientReceive_Start(),
ClientReceive_Finish(double("100")),
ClientSend(),
ServerReceive(),
ClientSend(),
ServerReceive(),
ClientClose(),
ServerCloseConnection(),
ServerClose()
)
)
This test succeeded because the server didn’t send 100 until the last message.
After a few more random test runs, ct executes a run that fails, revealing the
defect.
This example shows that a random test strategy generates a lot of test runs easily;
it is no more work for us to set /nruns:1000. But many of those randomly generated
runs do not exercise the implementation thoroughly, so in this example the built-in
random strategy does not achieve good coverage rapidly. We can often do better
by programming our own strategy, which we can load into ct with the /strategy
option. The following sections show how.
more free ebooks download links at:
http://www.ebook-x.com