So you've spent some tme becoming more aware of quality and what quality means. You've been looking at the differences between a Mercedes and a Hyundai. You've also started reading up on quality and on engineering. Great start! What's next? Well, the next step is to realize you need to look beyond the stated requirements and dig deeper.
In my opinion, functional or business requirements docs are like nets. They catch a lot of 'big stuff' but they can easily let little--albeit important--stuff through. For instance, a business requirement might be that a tax calculation be performed on a per-item basis. t the same time, it might not mention that the overall tax rate, which is rounded to the lowest cent, needs to be calculated on the total purchase and not the individual items.
I have no idea what the rules are for tax calculation. I don't test it, never have. And even if I did know, it'd only be specific for the US. So please - look over the details in this example and try to recognize the key point...
The Tax Man Cometh
As an example, assume a user buys one $0.55 candy bar, a $1.75 bag of chips, and a $4.27 bottle of antacid. At 10% tax, that would look something like this:
Tax is calculated on each item, and in all cases is rounded down to the lower cent.
However, if you factor tax on the sub-total of the items, it may actually be more! The subtotal of these three items is $6.57, and tax is $0.65. Calculated this way, the total is actually $7.22.
OK - I agree. This is a case of a missed business requirement. But this is a great example of how a tester needs to be on his or her toes, asking questions and always exploring for what can go wrong.
Not Another Bad Lego!
I'll take a manufacturing flaw as another example, which hopefully you can extrapolate to software quality. I have three sons, spanning just 4 years, and as a family (Mom is the ringleader here), we are Lego entusiasts. Birthday presents are almost always Legos - these days, they are super-complex Star Wars sets. Whenever my boys have saved up $10 or so, we're off to the store to buy a new Lego. Several times in the past couple months, we have picked up Legos with one of two problems: 1) missing peices and 2) poor fit. There's nothing more frustrating for a kid than to have their new Lego missing a critical piece--or for the parent who has to drive 20 miles to return the Lego!
I'm sure there's a manufacturing QA requirement here that each individual bag of pieces has a certain total weight. That's how they make sure all the pieces get into the box (how they miss a piece on this test is beyond me). Two days ago, my youngest bought himself a new Bionicle, only to find that the Bionicle's shoulder-claw (you have to see one to understand) was in the box but it didn't stay in place. Turns out, a manufacturing flaw caused the shoulder claw's insert tab to be too small, producing insufficient friction for it to stay.
So as a QA engineer at Lego, I'm sure I'd be dealing with the requirement to have all the parts in the box. But would I be asking about how we ensure EACH part shipped in EACH package has the right fit? That's going beyond the requirements.
Hey, You Stole My Car (Analogy)
OK, one last analogy and I think the point will be well-clarified. Let's pretend you are responsible for quality for an automobile. The requirements are that it be capable of a certain miles per gallon (KMPL), that it run for so many successive hours, and that it fit so many passengers. So let's assume these are 25 MPG, a service life of 100,000 operating hours, and it seats 4.
In the early 80's, AMC made a car called the Pacer. It was small, rather fuel efficient, and cheap. It sat five (although we had many more than that in my friend's Pacer once). Service hours? My friend Kate couldn't kill it, no matter how hard she tried - she drove it for a year without putting oil in it!
A colleague of mine at Microsoft recently had to buy a car. He chose a VW Toureg V10 diesel. He actually hits 30, 35 MPG. The car has a proven service life well in excess of 100,000 hours and it fits 5 (very comfortably, I might add). Which car is of higher quality? Why?
I'll leave you with that thought. Dig deeper, go beyond the stated requirements. It's the difference between an Ambassador and a Skoda, a Pacer and a Toureg.