I wrote a simple scanning code using WIA. I don't have a scanner device so I can't test it. Can I simulate a WIA device to testing it ?
With enough effort and the WIA SDK (and probably the Windows DDK as well) you probably can. But it will be a large amount of effort, especially compared to the price tag of a cheap scanner.
I'm assuming your time is worth something. If this is a hobby project, then compare the price of a cheap scanner to the time saved that can be spent working on the fun parts of the project. If this is a work project, then the time saved is more valuable to your customer than to you, but there should still be business case for buying hardware that will save more time than it cost.