One of the major components of the testing arsenal is finding combinations of inputs that cause problems in the AUT.

For all but the most trivial applications, the number of possible input combinations is somewhere between daunting and infinite.
To get around this, many testers subscribe to Pairwise testing - the argument being that most troublesome combinations arise from simple pairs of inputs, rather than deeply nested combinations. This is not to deny the presence of properly obscure bugs, it is merely a technique to direct testing to where it is most likely to produce results soonest. It is left to your own discretion, experience and knowledge of the AUT to extend the pairwise test cases with your own exploratory testing.

The creation of pairwise tests is a fascinating mathematical exercise. Luckily a team at Microsoft (again?!) have produced PICT to do the hard maths.

It works very well but some people fear the command line, so I produced an Excel spreadsheet as a front end:

The PICTinput sheet allows you to enter test input names and possible values:

PICTinput
OS XP Vista W2K3 W2K8 W2K3_64 W2K8_64 W7RC1
Security Local Network Inadequate Botched Swiss Cheese Microsoft Standard
Install New Upgrade Confused Impossible Frustrating
Killbits Installed? YES NO WTF??!!?!? NEARLY
Change Folder? NO YES MAYBE
User Admin N00b Super User Super Duper User Super Smashing Great

The Control sheet allows you to set the combination depth (e.g. 2 to test by pairs) and output file name.
Pressing the button invokes the following VBA routine, which passes the PICTinput values to the PICT CLI. 


Sub Button1_Click()
    
'create text version of inputs sheet
    Worksheets("PICTinput").Activate
    Set fs = CreateObject("Scripting.FileSystemObject")
    Set a = fs.CreateTextFile("PICTinputs.txt", True)
    Dim newrange As Range
    For irow = 1 To ActiveSheet.UsedRange.Rows.Count
        pictLine = ""
        Set newrange = Intersect(Cells.Rows(irow), ActiveSheet.UsedRange)
        For Each cell In newrange
            If (cell.Column > 2) And (cell.Text <> "") Then
                pictLine = pictLine + ","
            End If
            pictLine = pictLine + cell.Text
            If cell.Column = 1 Then
                pictLine = pictLine + ":"
            End If
        Next cell
        a.WriteLine (pictLine)
    Next irow
    a.Close
    Worksheets("Control").Activate

'delete existing output
    Dim x As String
    Dim OutputFileName As String
    OutputFileName = ActiveSheet.Range("OutputFileName").Text
    
    ChDir (ThisWorkbook.Path)
    x = Dir(OutputFileName)
    If x <> "" Then
        If MsgBox("Overwrite existing output file " & OutputFileName & "?", vbYesNo + vbExclamation) = vbNo Then
            End
        Else
            Kill (OutputFileName)
        End If
    End If
    
'run PICT to create the test cases
    Dim ComboDepth As Integer
    
    ComboDepth = ActiveSheet.Range("Combination_Depth").Text
    Call Shell("cmd /C pict PICTinputs.txt > " & Chr(34) & OutputFileName & Chr(34) & " /o:" & ComboDepth)

'check that the output file exists
    x = Dir(OutputFileName)
    Do While x = ""
        Application.Wait (Now + TimeValue("0:00:1"))
        x = Dir(OutputFileName)
    Loop
    
'open the output and tidy the formatting
    Workbooks.Open (OutputFileName)
    Range("1:1").Cells.Font.Bold = True
    ActiveSheet.Columns.AutoFit
    
End Sub

and you end up with a table of test cases like this, covering every pair of input conditions:

pairwise test cases
OS Security Install Killbits Installed? Change Folder? User
W2K8_64 Swiss Cheese Upgrade WTF??!!?!? NO N00b
XP Network Upgrade YES MAYBE Super Smashing Great
W2K8_64 Local Confused NEARLY YES Super User
W2K3_64 Inadequate New NO MAYBE Admin
Vista Botched Frustrating NO NO Super Duper User
W7RC1 Local Impossible YES NO Super Smashing Great
XP Local Impossible NO YES N00b
W2K8_64 Microsoft Standard Impossible WTF??!!?!? MAYBE Super Duper User
W7RC1 Network Frustrating WTF??!!?!? YES Super User
W2K3_64 Botched Upgrade YES YES Super User
W2K3 Botched Confused NEARLY NO Admin
W2K8 Botched New NEARLY MAYBE Super Smashing Great
W2K3_64 Local Frustrating NEARLY MAYBE Super Duper User
W2K8_64 Botched New YES YES Admin
Vista Network Confused NEARLY MAYBE N00b
W2K8 Inadequate Confused YES YES Super Duper User
W7RC1 Botched New WTF??!!?!? MAYBE N00b
W7RC1 Microsoft Standard Upgrade NO NO Admin
XP Swiss Cheese New NEARLY NO Super User
W2K8 Network Impossible NO NO Admin
XP Inadequate Confused WTF??!!?!? NO Super Smashing Great
XP Botched Upgrade NEARLY YES Super Duper User
W7RC1 Swiss Cheese Frustrating YES MAYBE Super Duper User
W2K3 Local New NO YES Super Smashing Great
Vista Microsoft Standard Impossible YES YES Super User
W2K8 Local Frustrating WTF??!!?!? NO Admin
XP Microsoft Standard Frustrating NEARLY MAYBE N00b
W2K3_64 Network New WTF??!!?!? NO Super Duper User
Vista Inadequate Upgrade NEARLY MAYBE Super User
W2K8_64 Network Frustrating NO MAYBE Super Smashing Great
Vista Local New WTF??!!?!? YES Admin
W2K3 Swiss Cheese Confused NO YES Super User
W2K3 Network Impossible YES MAYBE N00b
W2K3 Microsoft Standard Upgrade WTF??!!?!? YES Super Duper User
W2K8 Swiss Cheese Impossible NEARLY NO Super Smashing Great
Vista Swiss Cheese Frustrating YES NO Super Smashing Great
W2K8_64 Inadequate Frustrating NO MAYBE N00b
W2K8 Local Upgrade NEARLY MAYBE N00b
W2K3 Inadequate Impossible NEARLY NO N00b
W2K8 Microsoft Standard Impossible WTF??!!?!? YES Super User
W2K3_64 Microsoft Standard Impossible YES NO Super Smashing Great
W2K3_64 Microsoft Standard Confused NEARLY NO N00b
W7RC1 Inadequate Confused NEARLY YES Super Smashing Great
XP Microsoft Standard New WTF??!!?!? NO Admin
W2K3_64 Swiss Cheese Frustrating YES YES Admin
XP Botched Impossible WTF??!!?!? NO Super Smashing Great
W2K3 Network Frustrating YES MAYBE N00b