Testing shows presence of defects: Testing may show the defects are present, but cannot prove that there are no defects. After testing the system or product thoroughly we cannot say that the product is complete defect free. Testing always reduces the no of undiscovered defects remaining in the software.
Exhaustive testing is impossible: Testing everything including all combinations of inputs and preconditions is not possible.We can use risks and priorities to focus testing efforts. for eg. If we are checking calculator application, we will check the basic functionality, Avoid to check all the combinations like 1+2, 1+3, 1+4…. and so on, It will take too much time to test. Hence we have to test only focus on risks and priorities.
Early testing: In the SDLC (software development life cycle) testing activities should start as early as possible and should focus on objectives Because defect gets early it will cost low to fix and vice versa.
Defect clustering: A small number of modules contains most of the defects found during pre release testing or shows the failures.
Pesticide paradox: If the same tests are repeated again and again, eventually the same set of test cases will no longer be able to find any new bugs. To overcome this “Pesticide Paradox”, it is important to review the test cases regularly and new and different tests need to be written to exercise different parts of the software or system to potentially find more defects.
Testing is context dependent: Testing is context dependent. Different kinds of sites are tested differently. For eg., safety and critical software are tested differently from an e-commerce site.
Absence of errors fallacy: If you have created software which does not fulfill user’s need or it is not built as per requirement, then finding and fixing defects does not help.