like a credit and debitoperation, always keeping the balance.Consistent test suites and customer business rules knowledge:those will be the main assets of what is called software factory (terminologythat I, personally, dislike, but this is another history...).Challenge Howto build a complete test suite for an existing code base when this was not donein the past at all. What is the size of effort that we are talking about? Howto appropriate this cost? Where are you going to recover this investment?Well, all activities, in a company, have two aspects tobe considered:The first the activity itself, the technical need andbenefit. The other, of course, financial investment, benefits, pays back etc. Let s discuss it further. ROI calculation:How to calculate the gain and the losses of TTD, to see if it worth the effort?The main point of analysis is to verify how slower development goes after TDD implementation and how much this additional period costs.We have, at first, to assume that TDD development goes slower than conventional development.In principle, delivery 0 (D0) is happening later, but this time is to be recovered later in QA (Quality assurance phase). This would be a consequence of the fact that QA phase with last defects can be finalized earlier. Defects use to be blockers for future test cases execution. So while certain defects are no solved, QA phase, or part of these phase is put as on hold.This will happen as an ongoing process, after TDD has been adopted.However, major challenge, is how to cover initial investment on TDD.Consider that, for the set of applications that your team is developing there is no test suite prepared, at all. It will be, most likely, not possible to recover such investment in a project life time. However, since most of development organizations doesn t have any other funding source than projects themselves, test suites are to be built in parts, in a per project basis.What about investment return?ROI = Project Life Cycle Reduction investment ________________________________________________________ investment Time is money. If we do consider Life Cycle reduction, of course, without additional resources, there will be cost savings.The investment will be the additional effort allocated in a given project for Test Cases preparation, for the coverage of Use Cases implemented in such project.But how to measure benefit of existing test suite? How to evaluate benefits of composition, project by project, of a consistent test suite that is to be completely run, as soon as project starts. This is an important asset that will be incorporated to development organization.Investment returns calculation in project organizations is not an easy model because return doesn t necessarily goes to project itself but to the organization as a whole. So benefits are to reflect In future projects,Benefits of quality:Cost savings, during project (life cycle reduction)+Cost savings for product sustain.+Image damage savings.______________________________________________________________References[1] W. Humphrey. A discipline for software engineering.Addison-Wesley, 1997.[2] M. MAuller and O. Hagner. Experiment about test- rstprogramming. IEE Proceedings Software, 149(5):131{136, Oct. 2002.[3] M. MAuller and F. Padberg. Extreme programming froman engineering economics point of view. In InternationalWorkshop on Economics-Driven Software EngineeringResearch (EDSER), Orlando, Florida, May 2002.[5]