UML Weekend Crash Course™ - To Parent Directory

90
Saturday Morning
In Figure 8-6, you identify the fourth scenario by continuing from the “Any unfilled
quantities” decision of Scenario 1. But this time choose the path where there are unfilled
quantities. Following this path tells you to create a backorder before the scenario ends. This
segment is Scenario 4.
Scenario 1
[True]
Any unfilled
quantities
[Yes]
[No]
Create Back
Order
Scenario 4
Figure 8-6 Scenario 4
The goal of developing scenarios is to account for every logical possibility in the flow of
the Use Case. Every segment identifies a unique line of logic within the total Use Case.
But you’re not done yet.
Applying Use Case scenarios
Technically, the definition of a Use Case scenario says that each scenario describes a single
logical path through a Use Case. Using the Activity diagram, you can visually identify each
path simply by following the connecting lines in the diagram. But in the Fill Order Use Case
example, each individual arrow traces a separate logical segment, not necessarily a complete
logical path, from the beginning of the Use Case to the end of the Use Case. For example,
alternative Scenario 3 only identified the steps that were unique from those already identified
by Scenario 1.
I did not show repeated segments of paths already singled out by a previous scenario.
This convention is a common one employed to avoid redundancy and extra work. When I
write the formal scenarios, or test cases, I simply build the test case from the scenario segments.
By doing a little mixing and matching, I can provide comprehensive coverage of
every combination. For example, to fully specify Scenario 2, I would include the first two
steps and the decision from Scenario 1 plus the unique steps of Scenario 2.
Note too that, whenever you encounter a loop, the scenario maps out only a single pass
through the loop. To test the loop thoroughly, run the scenario segment multiple times,
remembering to test the boundary conditions.