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Today one of our test engineers, Manfred, presented about systematic identification of test values. One of the topics were decision tables. I was fascinated how easy he created tables with all possible combinations. Here is how:

1. Write the conditions in seperate rows.

Condition A
Condition B
Condition C

2. Now make 2^n columns where n is the number of conditions.

Condition A |   |   |   |   |   |   |   |   |
Condition B |   |   |   |   |   |   |   |   |
Condition C |   |   |   |   |   |   |   |   |

3. Start at the bottom condition and write alternating Y and N.

Condition A |   |   |   |   |   |   |   |   |
Condition B |   |   |   |   |   |   |   |   |
Condition C | Y | N | Y | N | Y | N | Y | N |

4. Fill the next row with alternating Y Y N N …

Condition A |   |   |   |   |   |   |   |   |
Condition B | Y | Y | N | N | Y | Y | N | N |
Condition C | Y | N | Y | N | Y | N | Y | N |

5. Each row you double the number of consecutive Ys and Ns.

Condition A | Y | Y | Y | Y | N | N | N | N |
Condition B | Y | Y | N | N | Y | Y | N | N |
Condition C | Y | N | Y | N | Y | N | Y | N |

6. Do so until all rows are filled.
7. Now you can add your decisions to the table.

Condition A | Y | Y | Y | Y | N | N | N | N |
Condition B | Y | Y | N | N | Y | Y | N | N |
Condition C | Y | N | Y | N | Y | N | Y | N |
---------------------------------------------
Decision 1  |   | X | X |   |   |   |   |   |
...

Using this algorithm you can be sure you covered all combinations. It doesn’t matter how many conditions you have and you don’t even have to think

Thanks Manfred!

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Tags: decision tables, testing

This entry was posted on Friday, March 27th, 2009 at 21:44 and is filed under software development, testing. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.