Decision Tables

The techniques of equivalence partitioning and boundary value analysis are often applied to specific situations or inputs.

However, if different combinations of inputs result in different actions being taken, this can be more difficult to show using equivalence partitioning and boundary value analysis, which tend to be more focused on the user interface. The other two specification-based software testing techniques, decision tables and state transition testing are more focused on business logic or business rules.

A decision table is a good way to deal with combinations of things (e.g. inputs). This technique is sometimes also referred to as a ’cause-effect’ table. The reason for this is that there is an associated logic diagramming technique called ’cause-effect graphing’ which was sometimes used to help derive the decision table

Decision tables can be used in test design whether or not they are used in specifications, as they help testers explore the effects of combinations of different inputs and other software states that must correctly implement business rules.

The first task is to identify a suitable function or subsystem which reacts according to a combination of inputs or events. The system should not contain too many inputs otherwise the number of combinations will become unmanageable.

 It is better to deal with large numbers of conditions by dividing them into subsets and dealing with the subsets one at a time. Once you have identified the aspects that need to be combined, then you put them into a table listing all the combinations of True and False for each of the aspects.

Don’t just assume that all combinations need to be tested. It is always better to prioritize and test the most important combinations. Having the full table helps us to decide which combinations we should test and which not to test this time. In the example above all the conditions are binary, i.e. they have only two possible values: True or False (or we can say Yes or No).

TABLE 4 . 5 Decision table with additional outcomes:
Conditions Rule 1 Rule 2 Rule 3 Rule 4
Repayment amount has T T F F
been entered:
Term of loan has been T F T F
entered:

Actions/Outcomes
Process loan amount: Y Y
Process term: Y Y
Error message: Y


Ref: http://istqbexamcertification.com/what-is-decision-table-in-software-testing/