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How (Much) Do Developers Test?


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What do we know about software testing in the real world? It seems we know from Fred Brooks’ seminal work “The Mythical Man-Month” that 50% of project effort is spent on testing. However, due to the enormous advances in software engineering in the past 40 years, the question stands: Is this observation still true? In fact, was it ever true? The vision for our research is to settle the discussion about Brooks’ estimation once and for all: How much do developers test? Does developers’ estimation on how much they test match reality? How frequently do they execute their tests, and is there a relationship between test runtime and execution frequency? What are the typical reactions to failing tests? Do developers solve actual defects in the production code, or do they merely relax their test assertions? Emerging results from 40 software engineering students show that students overestimate their testing time threefold, and 50% of them test as little as 4% of their time, or less.

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How (Much) Do Developers Test?

  1. 1. How (Much) Do Developers Test? Moritz Beller @Inventitech Andy Zaidman, Georgios Gousios, Annibale Panichella, Igor Levaja
  2. 2. Thou shalt not have less than 80% coverage
  3. 3. Brooks, 1975
  4. 4. 50% … of Project Effort Brooks, 1975
  5. 5. How (Much) Do You Test?
  6. 6. 34
  7. 7. Students
  8. 8. 4.2 yr
  9. 9. OMG!!!
  10. 10. Histogram of Testing Time 50% of students test only 4% of their time, or less
  11. 11. Thou shalt not have less than 75% coverage
  12. 12. Thou shalt not have less than 75% coverage Students
  13. 13. Estimated 27%
  14. 14. Estimated 27% Reality 9%
  15. 15. >1,000
  16. 16. 13 yr
  17. 17. Estimated 48%
  18. 18. Estimated 48% Reality 25%
  19. 19. 65% of test executions fail.
  20. 20. 50% of test failures are fixed within 10 minutes.
  21. 21. Image source:
  22. 22. Image source:
  23. 23. Nobody follows TDD (strictly). Image source:
  24. 24. @Inventitech Moritz Beller, TU Delft How (Much) Do Developers Test?
  25. 25. @Inventitech Moritz Beller, TU Delft How (Much) Do Developers Test?
  26. 26. @Inventitech Moritz Beller, TU Delft How (Much) Do Developers Test?
  27. 27. @Inventitech Moritz Beller, TU Delft How (Much) Do Developers Test?