smashing.org

Unless you're working at a very young company or only work on new projects, you will undoubtedly run into legacy systems some point. These are systems that you didn't design, that nobody else understands, are likely poorly documented, and are now your responsibility to maintain. I just migrated such a system from one data center to another, and tested it. It worked for my test scenarios. In the real world? BOOM! Utter disaster. I found the problem, but that doesn't make me feel any better -- I have a lot of pride in the quality of my work. Unfortunately, even with documentation, you can't possibly understand every little nuance of systems you didn't design. Unless your testing methodologies are akin to those of NASA (and I've been through test plans like that), something is very likely to go wrong.

So, two lessons to take away from this:

• Always run your final tests in a production-like environment.
• EXPECT PAIN!