I once had this fun contract to fix code in one giant application written in PHP. The org of decent size who wrote said code in a first place had code reviews,

I once had this fun contract to fix code in one giant application written in PHP. The org of decent size who wrote said code in a first place had code reviews, unit tests and what not. The end result was that they had to hire outside person to fix what they have produced. I looked through the software and noticed whole bunch of iffy patterns. Ended up writing giant Python script that searched said patterns and fixed it where possible marking with appropriate comments and issued a warning comments where it could not. Not sure if this is a regular occurrence in companies that write and maintain their internal software as this was the only time I did job like this.