Back when I was the "new guy" code monkey at a fairly sizeable brick-and-mortor-and-e-retailer, I let the intrusive thoughts win and did some impromptu QA on the e-commerce site. (In the test environment. Don't worry.)
It handled things like trying to put "0" or "-1" or "9999999999999" or "argyle" quantity of an item in the cart just fine.
But I know my 2's-compliment signed integers. So I tried putting "0xFFFFFFFF" quantity of an item in my cart. Lo and behold, there was now -1 quantity of that item in my cart and my subtotal was also negative. I could also do things like put a $100.00 thing in the cart and then -1 quantity of something that cost $99.00 in the cart and have a $1.00 subtotal.
(IIRC, there was some issue with McDonalds ordering kiosks at one time where you could compose an order with negative quantities of things to get an arbitrarily large unauthorized discount.)
The rest of my team thought I was a fucking genius from that moment on. I highly recommend if you're ever the "new guy" dev on a team and want to appear indispensible, find a bug that it would never occur to a QA engineer who doesn't have a computer science degree to even test for.
A long time ago I was the guinea pig/first user for a company developed system.
I often had my 1 year old at the time son with me when I worked on the weekend. He had a great time smashing buttons on the keyboard and randomly clicking the mouse on the test version. He found most of the bugs.
To be fair, the team at the time was all business majors. (Is "Computer Information Systems" what they call that degree most places or just at my alma mater?) I think I was the only computer science major there.
They'd done a surprisingly admirable job of cobbling together a working e-commerce, loss prevention, customer sercvice portal, orderfulfillment, and CMS suite. And their schooling was in, like, finance, MS Office, and maybe one semester on actual programming.
None of them had ever learned how to count in binary. Let alone been exposed to 2's compliment. And there were no QA engineers.
Oh, there was the sysadmin. He had a temper and was a cowboy. If you asked him to do something, it'd be fuckin' done, man. But you did not want to know how he made sausage. The boss asked him to set up a way for us to do code reviews and he installed Atlassian Fisheye/Crucible on a laptop under his desk. We used that for years. And a lot of the business logic of the customer-facing e-commerce site lived in the rewrite rules in the Apache config that only he had access to and no one else could decipher if they did have access.
The McDonalds thing was simple. 90 cent burger, minus cheese, was -10 cents. Or something along that way. Basically the "hold the cheese" value was fixed but they forgot some items with cheese are piss cheap.
As a PO I'm usually asking QA for some tests that actually show the product meets the requirements
There might be 50 pages proving it rejects bad input, and nothing showing it can successfully handle a perfectly correct case. We seem bad at training testers.
That sounds strange. I cannot comment on your particular case without seeing the test artifacts.
Generally speaking, there is nothing wrong with tests that ensure bad input doesn't break the system, as this can easily lead to incorrect system states, damage to the environment, loss of data, money, reputation, and even lives - although most systems are not critical enough to threaten lives.
You wouldn't need QAs if you only needed to validate that the product meets the requirements. In a typical company, many people are involved in that process. This includes the developer who wrote the code, the developer who reviewed it, and the people who conduct acceptance testing, among others. If your developers produce code that doesn't meet the requirements, you're in trouble.
I'm not saying that QA shouldn't validate whether the system meets the requirements, but you don't want them to do just that.
Doesn't sound too weird to me. In my experience, devs always focus too much on positive / correct inputs, as they want things to work. Which is why you need testers that will catch all the weird crazy ways people can break things.
Testers shouldn't even see the code of it can't handle nominal cases.
I still fondly remember the QA guy on the first consumer electronics project I worked on. He didn't do scripting or test harnesses or dependency injection, he used the product and filed good bugs telling us what would fuck up our customer's expectations.
A good QA person helps with product design too if you let them.
Unfortunately the bar was built on long int so it overflowed 23 times and landed on about 1.2 billion.
One billion, two-hundred fifteen million, seven-hundred fifty-two thousand, two-hundred-something bottles of beer on the wall, one billion, two-hundred fifteen million, seven-hundred fifty-two thousand, two-hundred-something bottles of beer! Take one down, pass it around...