What are the principles of testing?

 

Principles of Testing

There are seven principles of testing. They are as follows:

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. For example: In an application in one screen there are 15 input fields, each having 5 possible values, then to test all the valid combinations you would need 30  517  578  125  (5¹⁵) tests. This is very unlikely that the project timescales would allow for this number of tests. So, accessing and managing risk is one of the most important activities and reason for testing in any project.

3) Early testing: In the software development life cycle testing activities should start as early as possible and should be focused on defined objectives.

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 depending: 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 fulfill the user’s needs and expectations then finding and fixing defects does not help.

When do defects in software testing arise?

 

Because of the following reasons the software defects arise:

1. The person using the software application or product may not have enough knowledge of the product.
2. Maybe the software is used in the wrong way which leads to the defects or failures
3. The developers may have coded incorrectly and there can be defects present in the design.
4. Incorrect setup of the testing environments.

To know when defects in software testing arise, let us take a small example with a diagram as given below.

We can see that Requirement 1 is implemented correctly – we understood the customer’s requirement, designed correctly to meet that requirement, built correctly to meet the design, and so deliver that requirement with the right attributes: functionally, it does what it is supposed to do and it also has the right non-functional attributes, so it is fast enough, easy to understand and so on.

 

With the other requirements, errors have been made at different stages. Requirement 2 is fine until the software is coded, when we make some mistakes and introduce defects. Probably, these are easily spotted and corrected during testing, because we can see the product does not meet its design specification.

The defects introduced in Requirement 3 are harder to deal with; we built exactly what we were told to but unfortunately the designer made some mistakes so there are defects in the design. Unless we check against the requirements definition, we will not spot those defects during testing. When we do notice them they will be hard to fix because design changes will be required.

The defects in Requirement 4 were introduced during the definition of the requirements; the   product has been designed and built to meet that flawed requirements definition. If we test the product meets its requirements and design, it will pass its tests but may be rejected by the user or customer. Defects reported by the customer in acceptance test or live use can be very costly. Unfortunately, requirements and design defects are not rare; assessments of thousands of projects have shown that defects introduced during requirements and design make up close to half of the total number of defects.