Pairwise testing: How to create the table?

Hello I have doubt regarding how to create the table for the pairwise testing. For 开发者_开发百科example if I have three parameter which can each attain two different values. How do I create a table of input with all possible combination then? Would it look something like this?

    | 1 2 3
 -----------
  1 | 1 1 1
  2 | 1 2 2
  3 | 1 1 2
  4 | 1 2 1

Does each parameter corresponds to each column? However since I have 3 parameter, which each can take 2 different value. The number of test cases should be 2^3 isn't it?

There's a good article with links to some useful tools here:

http://blog.josephwilk.net/ruby/pairwise-testing-with-cucumber.html

For the parameters: each column is a parameter, and each row is a possible combination. Here is the table:

    | 1 2 3
 -----------
  1 | 1 1 1
  2 | 2 1 1
  3 | 1 2 1
  4 | 1 1 2
  5 | 2 2 1
  6 | 2 1 2
  7 | 1 2 2
  8 | 2 2 2

so 2^3=8 possible combinations as you can see :)

For the values: each column is a value, and each row is a possible combination:

    | 1 2
 --------
  1 | 1 1
  2 | 2 1
  3 | 1 2
  4 | 2 2

They are 2^2=4 possible combinations. Hope it helps.

1) Please note that pair-wise testing is not about scanning exhaustively all possible combination of values of all parameters. Firstly, such a scanning would give you an enormous amount of test cases that almost no existing system could be able to run all of them. Secondly, pair-wise testing for a software system is based on the hope that the two parameters having the highest number of possible values are the culprit for the highest percentage of faults of that system.

This is of course only a hope and almost no rigorous scientific research has existed so far to prove that.

2) What I often see in the documentations discussing pair wise testing, like this is that the list of all possible values (aka the pair-wise test table) is not constructed in a well thought way. This creates confusions.

In your case, all the parameters have the same number of possible values (2 values), therefore you could choose any two parameters of those three to build the table. What you could pay attention is the ordering of the combination: you iterate first the top-right parameter, then the next parameter to the left, and so on, ...

Say if you have two parameters p1 and p2, p1 has two possible values apple and orange; and p2 has two possible values red and blue, then your pair-wise test table would be:

index| p1     p2
------------------
   1 | apple  red
   2 | apple  blue
   3 | orange red
   4 | orange blue