2 Why We Need Model-Based Testing

Systems with Finite Models 125
0 C()
A()
1
B(2)
C()
2 C()
Figure 7.9. Loop extension of model program M1.
0 A()
B(_) C()
1
A()
Figure 7.10. Loop extension of model program M2.
Each state in the product is a pair state formed from a state in M1 and a state in M2
(Figure 7.11). Form the initial pair state (0, 0) from the initial states of M1 and M2.
Generate the rest of the product by exploring from the initial pair state. Each action
that is enabled in a pair state must be enabled in both corresponding states in the loop
extensions of both programs. Here action A() is the only action which is enabled
in the initial states of both programs; C() and B( ) are only enabled in M1 and M2,
respectively. Executing action A() makes the transition to state 1 in M1 and makes a
self-loop transition back to state 0 in M2, so in the product A() makes the transition
to the pair state (1, 0). In this state, B(2) is enabled in M1 and B( ) is enabled in
M2. These two actions match because their names are the same, and a placeholder
matches any argument; here the placeholder in B( ) matches the argument in B(2).
These actions make transitions to states 2 and 1 in M1 and M2 respectively, resulting
in the pair state (2, 1) in the product. The action which appears in the product is B(2),
not the action B( ) with the placeholder. In the pair state (2, 1), C() is enabled in both
programs, making a final transition to the pair state (2, 0) in the product. In that pair
state, there are no actions that are enabled in both programs, so exploration stops;
more free ebooks download links at:
http://www.ebook-x.com