Here’s a very nice case study conducted at Microsoft on two projects:
http://research.microsoft.com/manuvir/papers/isese-fp17288-Bhat.pdf
Here are two tables showing the difference when using TDD
Table 1: Project A Outcome Measures
| Metric Description | Value |
| Actual defects/KLOC (using TDD) | X |
| Defects/KLOC of comparable team in org but not using TDD | 2.6X |
|
Increase in time taken to code the feature because of TDD (%) [Management estimates] |
25-30% |
Table 2 Project B Outcome Measures
| Metric Description | Value |
| Actual defects/KLOC (using TDD) | Y |
| Defects/KLOC of comparable team in org but not using TDD | 4.2Y |
|
Increase in time taken to code the feature because of TDD (%) [PM/DevLEAD/MGR estimates] |
15% |
I think that the numbers speak for themselves.
