When we are testing an application, we have to see the how the application behaves in various combinations of OS's, Platforms, etc.  The following table gives demonstrates that we have to test our app for the following combinations

There are 4*4*2*2*2 = 128 possible combinations for selecting 1 value for each of the above 5 parameters in combination with other e.g (Win XP, English, Installed, X86, 5.0) etc.

This takes a lot of time to test.  We can use pairwise testing to reduce the number of combinations and also achieve full coverage simultaneously.

Some goals of pairwise testing are

• Each value of each parameter is tested at least once
• Each variable in each parameter is tested in a pair with every variable in other parameters
• Pairs of variables that exist in other combinations can be dropped from the matrix of combinations

If we follow the above rules, we can reduce the number of combinations to 16.  

Luckily, we have tools that find the combinations for us and one such tool is PICT.  You can download PICT from http://download.microsoft.com/download/f/5/5/f55484df-8494-48fa-8dbd-8c6f76cc014b/pict33.msi

Also, this tool enables us to

• specify constains (eg. If CLR is installed, then we have to use IE 6.0)
• specify equivalent combinations (e.g. Japanese and German languages are likely to produce the same results).