Everywhere we look we can find some rules, some principles which give us some sense of security and make our life less chaotic.
Certain principles also apply to the world of testing.
They have been developed and formulated over the past fifty years but still provide us most accurate guidelines for all kinds of executed testes.
Anyway - if you are preparing for the ISTQB exam or a job interview for a tester you should be able to cite these principles even if you are woken up in the middle of the night!
Let’s get to know then the seven principles of testing according to the new ISTQB from 2018 year with some extra explanations.
Seven testing principles
No. 1 Testing shows the presence of defects, not their absence
Testing may show that there are some faults but cannot prove that software is free of defects.
Testing decreases probability of undetected defects in the software but even if no faults are found it doesn’t prove that the software is correct in one hundred percent.
No. 2 Exhaustive testing is impossible
It generally means that testing everything (all combination of entries and preconditions) is possible only in a reference to very trivial cases.
While describing scope of testing, instead of focusing on exhaustive testing, it’s better to take advantage of information about the risk and priorities.
No. 3 Early testing saves time and money
In order to detect faults as early as possible, testing should begin in the software development cycle or system as soon as possible and be directed to the execution of defined goals.
Testing activities should start:
- as early as possible
- only if it is possible in case of certain software
No. 4 Defects cluster together
Labour consumption of testing is divided proportionally to expected and observed defects density in the modules.
Small number of modules usually contain majority of defects found before the release or is responsible for majority of failures in the production.
It is associated with Pareto analysis:
In terms of quality improvement, a large majority of problems (80%) are produced by a few key causes (20%)
No. 5 Beware of the pesticide paradox
If the same tests are executed without any changes they soon will stop finding new defects.
To overcome the pesticide paradox tests have to be reviewed and updated regularly.
New, different test cases have to be designed in order to test different parts of software of system to allow finding new defects.
No. 6 Testing is context dependent
Testing is executed in different ways in different contexts. For example software critical for safety reasons will be tested in a different way then an online shop or banking system.
No. 7 Absence-of-errors is a fallacy
Finding and fixing bugs won’t help if the system doesn’t do for a user or doesn’t meet user’s requirements and expectations.
Even a product free of defects might not satisfy a user.