Writing Unit Tests in VBScript

Unit tests are important, although most of the cases you don’t get paid by writing unit tests, but they are there to make sure that your application works. Recently, I have to test a COM application in a outer process fashion. Thus I decide to write some unit tests in VBScript so in this way, the VBScript will be hosted/executed via cscript.exe. The VBScript will CreateObject and test the COM application.

How do you capture the error when tests in VBScript fail? You could write to a file, but you would need to tell the hosted testing agent where to look for this log file (probably a temp file). The easiest way would be to write to console (standard output) in VBScript so the testing agent just need to capture the output before the script ends.

In VBScript, you could use msgbox to show a dialog but this is not OK for testing purposes. You could also use WScript.Echo but depending on environment, the WScript object may not be available, and also may behave differently. i.e. Using wscript.exe to run the scripts, the WScript.Echo actually pops up a dialog.

The best way is to Create the Scripting.FileSystemObject and write to its standard stream.

Set Console = CreateObject("Scripting.FileSystemObject")
Console.GetStandardStream(1).WriteLine "https://helloacm.com"

So, we can emulate the Assert function like this:

Sub Assert(x, msg)
	If Not x Then
		' alternatively, you can throw Errors using Err.Raise
		Console.GetStandardStream(1).WriteLine msg 
	End If
End Sub

And you could run tests in VBScript like this:

pl1 = MyCOM.GetData(ax, ay, 10)
pl2 = MyCOM.GetData(ax, ay - 25, 7)
Assert pl1 < pl2, "pl1 < pl2"
Assert Len(MyCOM.ErrorMessage & MyCOM.WarningMessage) = 0, MyCOM.ErrorMessage & MyCOM.WarningMessage

All you have to do is to capture all output from your VBScript and fail the tests if the output is not empty.

Alternatively, you can use Err.Raise to throw exception-like errors in VBScript, so the above could be rewritten using a much simpler method:

Sub Assert(x, msg)
	If Not x Then
		Err.Raise 1, msg, msg		
	End If
End Sub

However, if you have the following statement:

On Error Resume Next

Then all exceptions will be caught and ignored unless you manually test for the Error Object, like this:

Assert False, "Generated Error"
If Err.Source <> "" Then
   Msgbox "Error: " & Err.Source
End If

–EOF (The Ultimate Computing & Technology Blog) —