1. A useful testing technique and more…
Decision Tables
A useful testing technique and more…
Marien de Wilde, Solution Architect

2. In this session … Definition Application areas
Steps to create a decision table
Exercise
Solution to exercise
February 2010

3. Definition Components
A decision table lists causes and effects in a matrix. Each column represents a unique combination.
Purpose is to structure logic
Cause = condition Effect = action = expected results
February 2010

4. Application Areas Business Analysis Programming Testing
Hardware Design
etc
February 2010

5. Steps to Create a decision table
List all causes in the decision table
Calculate the number of possible combinations
Fill columns with all possible combinations
Reduce test combinations
Check covered combinations
Add effects to the table
February 2010

6. Step 1: List all causes Hints:
Write down the values the cause/condition can assume
Cluster related causes
Put the most dominating cause first
Put multi valued causes last
February 2010

7. Step 2: Calculate combinations
If all causes are simply Y/N values: 2number of causes
If 1 cause with 3 values and 3 with 2: 31 * 23 = 24
Or, use the Values column and multiply each value down the column, eg. 3*2*2*2=24
Number of Values to the power of the number of causes with these values
February 2010

8. Step 3: Fill columns Algorithm:
Determine Repeating Factor (RF): divide remaining combinations by the number of possible values for that cause
Write RF times the first value, then RF times the next etc. until row is full
Next row, go to 1.
February 2010

9. Step 4: Reduce combinations
Find indifferent combinations – place a ‘-’
Often there are dependencies between causes. For example cause 1 can test if a field is entered (Y/N) and cause 2 can test if the same field is valid (Y/N). It is no use testing if the field is valid if it has not been entered.
Join columns: When in a column a cause is of no interest any more to determine the effects, a dash ‘-’ is placed in the column for that cause. This has to be done for both the column with a ‘Y’ and the column with a ‘N’. This makes the 2 columns identical and one of them can be deleted.
Join columns where columns are identical
Tip: ensure the effects are the same
February 2010

10. Step 5: Check covered combinations
Checksum
For each column calculate the combinations it represents
A ‘-’ represents as many combinations as the cause has
Multiply for each ‘-’ down the column
Add up total and compare with step 2
February 2010

11. Step 6: Add effects to table
Read column by column and determine the effects
One effect can occur in multiple test combinations
February 2010

12. Exercise: Specification Create a decision table
A mailing is to be sent out to customers. The content of the mailing is about the current level of discounting and potential levels of discounting. The content is different for different types of customers.
Customer Types A, B and C get a normal letter except Customer Type C, who get a special letter. Any customer with 2 or more current lines or with a credit rating of ‘X’ get a special paragraph added with an offer to subscribe to another level of discounting.
Ask questions from the analyst for clarification
February 2010

13. Solution on next slide
February 2010

14. Exercise: possible solution
“2 or more current lines OR credit rating X”. What if both: AND?
Other customer types? See “O-Other” above.
What about non current lines?
February 2010

15. Thank You
February 2010