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Software Testing
methodologyUnit -1
Introduction:purpose of testing,dichotomies,model fortestin
,conse uence of bu s
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The purpose of testing
The purpose of testing is to show thatprogram has bugs.
the bug is manifested in deviations from anexpected
behaviour
The purpose of testing is to show thatsoftware works.
The purpose of testing is to show thatsoftware doesnt works.
The purpose of testing is to reduce the riskof the software. The
purpose of testing is to know the
productivity and quality of the software
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Continued
1)Test and test design as a part of qualityassurance should also
focus on bugprevention.
2)To the extent testing and testing design
donot prevent the bugs , they should beable to identify the
symptoms caused by thebugs and finally tests should provide a
cleardiagnosis so that the bug can be easilycorrected.
3)Now bug prevention is the testings firstgoal.
->a prevented bug is better thandetected or corrected bu . If
the bu is
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Productivity and quality inftw r
1)once in a production of software everymanufacturing phase is
subjected to qualitycontrol and testing from component
sourceinspection to final testing before shipping . Ifflaws are
discovered at any stage , the widgetor the part of it will be
discarded or cycled backfor rework and correction.
2)Productivity is measured by the sum of costsof the
material,the rework,and the discardedcomponents and the cost of
quality assuranceand testing.
3)there is a trade off between quality assurancecosts and
manufacturing costs .
->insufficient effort is s ent in ualit
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->conversely ,if inspection is do good thatall faults are
caught as they occur ,inspection cost will dominate ,and again
netcosts will suffer.
4)The manufacturing process designersattempts to establish a
level of testing anda quality assurance , that minimizes a netcost
for the given quality objective.
5)Productivity and quality assurance for amanufactured items can
be low as 2% for aconsumer products or high as 80% in the
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Goals of the testing
1)As we discussed in the 3rd slide that bugprevention is the
primary goal rather thandetecting or correcting.
2)unfortunately we cant achieve this ideal,despite our efforts
there will be bugs as weare human.
3)to the extent that testing fails to reach itsprimary goal, bug
prevention ,it must go tothe secondary goal bug discovery.
4)bugs are not always obvious.
5)the test design must document
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Phases in testers mental life
While testing any software productThere is an attitudinal
progression intester , characterized by the following 5
phases. Phase 0:There is no difference in testing
and debugging , other than in supportof debugging testing has no
purpose.
Phase 1:the purpose of testing is toshow that software works
.
Phase 2:the purpose of testing is to
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Phase 3:the purpose of testing is notto prove anything , but to
reduce theperceived risk of not working to an
acceptable value. Phase 4:testing is not an act , its a
mental discipline that results in low
risks software without taking muchtesting effort.
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