The Role and Importance of Quality Assurance (QA)

There is a moment where the young and enthusiastic learn that seat-off-the-pants is quick but eventually leads to catastrophe. You can tell at which stage engineers are by asking them what they think of QA: if they think it's an occupation for the lesser divinities of programming, they aren't there yet; if they have enough experience, they will think of QA engineers as demi-gods whose verdict makes and breaks months of coding.

Having been on for decades, I am of course a very, very strong proponent of mandatory QA. To me, this last step in the development process fulfills three main goals:

1. Interface stability and security Making sure that the code does what it is supposed to do especially in boundary conditions that developers typically overlook. The most common scenario is that of empty data (null pointers, etc.) somewhere code assumes there to be an object, but testing code for SQL injections is another, perfectly invaluable example. This has nothing to do with the functionality of the code, but with its ability to behave properly in unusual conditions.
2. Performance and stress testing Checking how the code behaves under realistic scenarios and not in the simple case the developer faces. Instead of 5 users, make 500,000 run concurrently on the software and see what it does. Instead of 100 messages, see what the system does with 100,000,000. Instead of running on a souped up developer machine with a 25" display, look at your software from the point of view of a user with a $200 netbook.
3. User experience and acceptance Ensuring the flows make sense from the end use perspective. Feel yourself into the user and try performing some common tasks. See what happens if you try doing something normal, but atypical. For instance, try adding an extension to a phone number and see whether the software rejects the input.