Software Testing Principles

1. Testing shows presence of defects

Testing can show the defects are present, but cannot prove that there are no defects. Even after testing the application or product thoroughly we cannot say that the product is 100% defect free. Testing always reduces the number of undiscovered defects remaining in the software but even if no defects are found, it is not a proof of correctness.

2. Exhaustive testing is impossible

Testing everything including all combinations of inputs and preconditions is not possible. So, instead of doing the exhaustive testing we can use risks and priorities to focus testing efforts. So, accessing and managing risk is one of the most important activities and reason for testing in any project. However, if possible we can try to cover as many as combination as we want in order to gain the confidence.

3. Early testing

In the software development life cycle testing activities should start as early as possible and should be focused on defined objectives. Static Testing shall be performed.

4. Defect clustering

A small number of modules contains most of the defects discovered during pre-release testing or shows the most operational failures.

5. Pesticide paradox

If the same kinds of 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 really very 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.

6. Testing is context dependent

Testing is basically context dependent. Different kinds of sites are tested differently. For example, safety – critical software is tested differently from an e-commerce site.

7. Absence of errors fallacy

If the system built is unusable and does not fulfil the user’s needs and expectations then finding and fixing defects does not help. Don't proceed to test the unsuable system or when the software or system are deviated away from requirements.