At the end of 2008 I switched credit cards from provider X to provider Y, lured by the promises of untold wealth from the cashback deal they offered. However, I’m yet to have a month where using this card has gone smoothly: which makes me wonder how well their application and business logic has been tested.

It was all triggered by me setting up a direct debit to pay the card off each month, and I thought nothing more of it. I was therefore somewhat surprised when the next month no payment was taken and I was spanked for interest. I phoned up – and was informed that my direct debit had indeed been set up, but flagged to start in the year 8888. At first glance, this looks like a user error which the software should reject. But then you could argue that 8888 is a valid year – just a very unusual one to use in a direct debit.

So where do we mark the cutoff between sensible data entries and wrong ones? Can we implement fuzzy logic for such subjective testing? And if so, how can we guarantee repeatable behaviour between tests – which is critical for automated testing?

Anyway – the direct debit is now working, but this appears to have triggered me travelling down some sort of error path in the credit card company’s business logic. I’ve decided to stop using this card for 2 months to let the dust settle: and then perhaps I’ll test their business logic some more…