Fundamentals of testing 1

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The fundamentals of testing

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Fundamentals of testing 1

  1. 1. FUNDAMENTALS OF TESTING Hoang V. Nguyen startnewday85@gmail.com startnewday85.blogspot.com Dept. of Computer Science – FIT - HUATester Training Course
  2. 2. Tester Training Course 2011
  3. 3. Explorapedia, World of Nature, version 1.0Tester Training Course 2011
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  5. 5. Pepsi 349 Scandal Tester Training Course 2011
  6. 6. European Space Agency Ariane 5 After 37 ½ seconds, was destroyed $370 millionsTester Training Course 2011
  7. 7. London Ambulance ServiceTester Training Course 2011
  8. 8. What happened?Tester Training Course 2011
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  10. 10. What Failures’ effects?Tester Training Course 2011
  11. 11. What Failures’ effects?  Can harm: • people • companies • the environment  Can lead to: • Loss of money • Loss of time • Loss of business reputation • Injury • DeathTester Training Course 2011
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  14. 14. DEFECT FAULT BUGTester Training Course 2011
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  16. 16. Why do defects occur in products?  Made by human • Who know some thing, but not everything • Who have skills, but aren’t perfect ==> Who do make mistakes(errors)  Under pressure • deadline • complexity ( system , organization) • individual reasons ==> no time to check ==> systems may be incomplete ==> increased frequency of errorsTester Training Course 2011
  17. 17. Reliability and Defect  Reliability: the probability that software will not cause the failure of the system for a specified time under specified conditions Can a system be defect-free? Can a system be reliable but still contains defects? Is a ”defect-free” system always reliable? Tester Training Course 2011
  18. 18.  Error/Mistake a human action which produces an incorrect result  Defect/Fault/Bug a manifestation of an error in software  Failure deviation of the software from its expected delivery or serviceTester Training Course 2011
  19. 19. Error – Defect – Failure make Failure is an event; defect is a state of the software, caused by an errorTester Training Course 2011
  20. 20. When do defects arise in SD context? Mistakes Correct Correct Correct made in requirement requirement requirement requirement Designed to Designed to Mistakes Designed to meet meet make in meet requirement requirement design requirement Built to meet Mistakes Built to meet Built to meet design make in built design design Product Wrong Product has Product has works as product bugs in it design flaws expected deliveredTester Training Course 2011
  21. 21. What does It cost to fix a defect?Tester Training Course 2011
  22. 22. Question A bug or defect is:A mistake made by a person;A run-time problem experienced by a user;The result of an error or mistake;The result of a failure, which may lead to an error? Tester Training Course 2011
  23. 23. Question When what is visible to end-users is a deviation from the specific or expected behavior, this is called:An ErrorA faultA FailureA defectA mistake Tester Training Course 2011
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  25. 25. Question Debugging is:Testing/checking whether the software performscorrectly;Checking that a previously reported defect has beencorrected;Identifying the cause of a defect, repairing the codeand checking the fix is correct;Checking that no unintended consequences haveoccurred as a result of a fix Tester Training Course 2011
  26. 26. Why is testing necessary?Tester Training Course 2011
  27. 27. Why is testing necessary? Because software is likely to have faults To learn about the reliability of the software To fill the time between delivery of the software and the release date To prove that the software has no faults Because testing is included in the project plan Because failures can be very expensive To avoid being used by customers To stay in businessTester Training Course 2011
  28. 28. Testing and Quality  Quality: get the satisfaction of all stakeholders Time Budget Quality Satisfy customers Technically excellent  Testing help us to measure and improve the quality of software • give confidence in the quality of softwareTester Training Course 2011
  29. 29. What is testing? The process consisting of all lifecycle activities, both static and dynamic, concerned with planning, preparation and evaluation of software products and related work products to determine that they satisfy specified requirements, to demonstrate that they are fit for purpose and to detect defects This is a suitable definition of testing for any level of testing. Tester Training Course 2011
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  31. 31. How much testing is enough? Tester Training Course 2011
  32. 32. “Test everything” Avr. 4 menus 3 options / menusystem has Average: 10 fields / screen20 screens 2 types input / field (date as Jan 3 or 3/1) (number as integer or decimal) Around 100 possible values Total for exhaustive testing: 20 x 4 x 3 x 10 x 2 x 100 = 480,000 tests If 1 second per test, 8000 mins, 133 hrs, 17.7 days (not counting finger trouble, faults or retest)Tester Training Course 2011
  33. 33. Question What is exhausive testing?When all the testers are exhausted;When all the planned tests have been executed;Exercising all combinations of inputs andpreconditions Tester Training Course 2011
  34. 34. Question How much time will exhaustive testing take? Infinite time; No much time; Impractical amount of time.Tester Training Course 2011
  35. 35. How much testing is enough? Testing principle Exhaustive testing is impossible Testing everything (all combinations of inputs and preconditions) is not feasible except for trivial cases. Instead of exhaustive testing, we use risks and priorities to focus testing efforts. Tester Training Course 2011
  36. 36. How much testing is enough? It’s never engough; When you have done what you planned; When your customer/user is happy; When you have proved that the system works correctly; When you are confident that the system work correctly; It depends on the risk for your system.Tester Training Course 2011
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  38. 38. RISK and TESTING  The number of test depends on RISK • RISK of missing important faults • RISK of incurring failure costs • RISK of releasing untested or under-tested software • RISK of losing credibility and market share • RISK of missing a market window • RISK of over-testing, ineffective testing  use RISK to determine: • what to test first • what to test most • how thoroughly to test each item • What not to test (this time)  use RISK to: • Allocate the time available for testing by prioritising testing ... Tester Training Course 2011
  39. 39. When can we meet our test objectives? Testing principle Early testing Testing activities should start as early as possible in the software or system development life cycle and should be focused on defined objectives. Tester Training Course 2011
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  41. 41. Is the software defect free? Testing principle Testing shows presence of defects Testing can show that defects are present, but cannot prove that there are no defects. Testing reduces the probability of undiscovered defects remaining in the software but, even if no defects are found, it is not a proof of correctness. Tester Training Course 2011
  42. 42. How are defects distributed? Testing principle Defect clustering A small number of modules contain most of the defects discovered during pre-release testing or show the most operational failures. Tester Training Course 2011
  43. 43. The defect clusters change over time Testing principle Pesticide paradox If the same tests are repeated over and over again, eventually the same set of test cases will no longer find any new bugs. To overcome this pesticide paradox, the test cases need to be regularly reviewed and revised, and new and different tests need to be written to exercise different parts of the software or system to potentially find more defects.Tester Training Course 2011
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  45. 45. Testing principle Absence-of-errors fallacy Finding and fixing defects does not help if the system built is unusable and does not fulfill the users needs and expectations.Tester Training Course 2011
  46. 46. Testing principle Testing is context dependent Testing is done differently in different contexts. For example, safety-critical software is tested differently from an e-commerce site.Tester Training Course 2011
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  48. 48. Question Which statement is most true?Different testing is needed depending upon theapplication.All software is tested in the same way.A technique that finds defects will always finddefects.A technique that has found no defects is not useful. Tester Training Course 2011
  49. 49. Question When is testing complete? When time and budget are exhaused. When there is enough information for sponsors to make an informed decision about release. When there are no remaining high priority defects outstanding. When every data combination has been exercised successfully.Tester Training Course 2011
  50. 50. • Why testing is necessary? • Failure, Fault, Bug, Defect, Error, Mistake • What is testing? • 7 general testing principles • Testing and Reliability • Testing and Quality • Testing and DebuggingTester Training Course 2011

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