We all are onboarded with the fact that "The more we test a software the more quality emerged". Proper testing is one of the key attributes of high-quality software.

1. TDD in Product Development
Beroza Paul
Sr. software engineer

2. Truth about Software Product Development
● Industry average experience is about 1-25 bugs per 1000 lines of code for
delivered software.
● 7-12 bugs per 1,000 lines of code find their way to the customers
● Fixing a bug takes 30 times longer than writing a line of code
● 75% of a developer’s time is spent on debugging (1500 hours a year!)
Source: Code Complete by Steve McConnell

3. Production Bug is Expensive!
● Fixing a production bug may cost 100x more than fixing a bug at
design time.
● Fixing a production bug may cost 15x more than fixing a bug at
implementation time.
Source: The Economics of Software Quality

4. Relative Costs of Fixing Bugs

5. How to reduce this cost?

6. Facts of Production Bug
● Most production bugs caused by simple programming mistakes
● 58% of them are trivial and can be addressed with test coverage
● Tiny mistakes will have huge impact on production

7. How to reduce trivial bugs?

8. Test Driven Development (TDD)?

9. TDD Life Cycle

10. TTD Reduces total cost?
Source: The Economics of Software Quality

11. TTD Results in Fewer Bugs?
● A case study of engineering teams at Microsoft and IBM showed that
the defect density decreased between 40% and 90% relative to similar
projects that did not use the TDD practice.
Source: Quality improvements

12. TDD Produces Better Quality?
● A study carried out among developers with 10+ years of professional
experience (on average), to investigate their perceptions when
employing TTD. Many of them agreed that “TDD allows greater quality
and maintainability”
Source: TDD analysis

13. TDD Promotes Simpler Design?
● The Department of Computer Science at North Carolina State
University, ran an experiment with two groups of programmers: one
used TDD and the other the linear approach.
● It turned out that “92% of developers believed that TDD yields higher
quality code, 79% thought that TDD promotes simpler design.
Source: TDD investigation

14. When TDD is wrong choice?

15. Developing GUI With TDD
● Trying to test the exact placement of UI components is pointless. First
because layout is subjective and should be "tested" by humans

16. TDD experience in team
● An enthusiastic team and at least one experienced developer who
knows how to write good tests and also knows a few things about
good architecture, otherwise think twice before going down the TDD
road.

17. TDD slows down initial process
● If you’re pressed for time and need to quickly launch your product or
solution, the TDD approach may not be your best choice

18. Test Code Requires Maintenance
● All lines of code require maintenance, which means cost. The cost is
easiest to acknowledge when a change to existing functionality is
made.

19. TDD approach is difficult
● In TDD we need mocks/stubs etc. When we start using mocks, after a
while, we will want to start using Dependency Injection (DI) and a
Inversion of Control (IoC) container. To do that you need to use
interfaces for everything. At the end we end up writing lot more code.

20. Thank you!

21. Reference
● https://www.youtube.com/watch?v=ln4WnxX-wrw
● https://fortegrp.com/test-driven-development-benefits15