Test Driven Development cost savings

Question

One of the biggest benefits of TDD is that defects are detected early in the development cycle and in the long term this will have significant savings for development costs.

I was wondering if anyone has come across a study that shows the cost of a defect at different stages of the development process? This of course could be a hypothetical cost or the actual cost ?

Answer 1

Here is a blog post I found that has some data on cost of bug fixes in different stages of the application development life cycle http://blog.programeter.com/post/1550840010/cost-of-bug-fixing-at-different-stages-of-sdlc

One thing to keep in mind is that these costs can very depending on the type of software, for example deploying a bug fix to a web application is going to have a significantly lower cost than a firmware update

Answer 2

I always refer to Scott Ambler's great graphs on the topic.

http://www.agilemodeling.com/essays/costOfChange.htm

The "Length of Feedback Cycle" shows where each practice impacts the cost of change curve. It's easy to see that the practices that result in quickest feedback are those that deliver the most benefit.