Decision table testing - TwoGears/hakomo-guides GitHub Wiki

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.

• Decision tables provide a systematic way of stating complex business rules, which is useful for developers as well as for testers.
• 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.
• It helps the developers to do a better job can also lead to better relationships with them. Testing combinations can be a challenge, as the number of combinations can often be huge. Testing all combinations may be impractical if not impossible. We have to be satisfied with testing just a small subset of combinations but making the choice of which combinations to test and which to leave out is also important. If you do not have a systematic way of selecting combinations, an arbitrary subset will be used and this may well result in an ineffective test effort.

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.
If we are applying this technique thoroughly, we would have one test for each column or rule of our decision table. The advantage of doing this is that we may test a combination of things that otherwise we might not have tested and that could find a defect. However, if we have a lot of combinations, it may not be possible or sensible to test every combination. If we are time-constrained, we may not have time to test all combinations. 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).