2 Why We Need Model-Based Testing

116 Structuring Model Programs with Features and Composition
15
ClientSend()
ServerCloseConnection()
25
21
ServerClose()
28
3
ServerClose()
29
2
0
ServerSocket() ClientSocket()
ServerBind() ClientSocket() ServerSocket()
5
ServerClose() 6
7
ClientSocket() ClientConnect()
11
ServerListen()
10
ServerClose()
ServerReceive() ServerSend(double("100"))
17
ServerCloseConnection()
ServerClose() ClientReceive_Start()
23
24
ClientReceive_Start()
22
13
12
ClientSocket()
8
ServerAccept()
18
ClientSend() ServerClose()
26
27
1
4
ServerListen()
ServerBind()
ServerClose()
ClientReceive_Finish(double("100"))
ClientReceive_Start() ClientReceive_Finish(double("100")) ClientReceive_Finish(double("99.9"))
ClientReceive_Finish(double("100"))
Figure 7.1. Client/server: true FSM.
ServerClose() ClientSocket()
31
ClientReceive_Start()
9
ServerClose()
ServerSend(double("99.9"))
16
ServerClose()
ServerCloseConnection() ClientReceive_Start()
ClientClose()
20
ClientSend() ClientClose() ServerClose()
ServerClose()
30
32
19
ClientReceive_Start()
ClientReceive_Finish(double("99.9"))
ClientReceive_Finish(double("99.9"))
ServerCloseConnection()
ClientClose()
14
ServerCloseConnection()
and Listen, and the client executes Socket. There are several runs where the client
Socket action is interleaved between different server actions. We know that all of
these runs have to be equivalent because the client and server do not even begin to
interact until the client’s Connect action. Before that, the order of the interleaving
of client and server actions cannot make any difference. Indeed, all of these runs
reach the same state. There are several other runs where the server executes Close
before the client connects. Nothing interesting can happen after that, so these runs
end in dead states. In the usual case where we want to see what happens after the
client and server connect, we could replace all of the runs in Figure 7.2 by a single
run without losing any useful information.
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