Formal definition:
Software testing is an empirical technical investigation conducted to provide stakeholders with information about the quality of the product or service under test, with respect to the context in which it is intended to operate.This includes, but is not limited to, the process of executing a program or application with the intent of finding software bugs.
Software quality:
Quality is not an absolute; it is value to some person. With that in mind, testing can never completely establish the correctness of arbitrary computer software; testing furnishes a criticism or comparison that compares the state and behaviour of the product against a specification. An important point is that software testing should be distinguished from the separate discipline of Software Quality Assurance (S.Q.A.), which encompasses all business process areas, not just testing.
The need for software testing:
Over its existence, computer software has continued to grow in complexity and size. Every software product has a target audience. For example, a video game software has its audience completely different from banking software. Therefore, when an organization develops or otherwise invests in a software product, it presumably must assess whether the software product will be acceptable to its end users, its target audience, its purchasers, and other stakeholders. Software testing is the process of attempting to make this assessment.
A study conducted by NIST in 2002 reports that software bugs cost the U.S. economy $59.5 billion annually. More than a third of this cost could be avoided if better software testing was performed.
Scope:
Software testing may be viewed as an important part of the software quality assurance (SQA) process.In SQA, software process specialists and auditors take a broader view on software and its development. They examine and change the software engineering process itself to reduce the amount of faults that end up in defect rate. What constitutes an acceptable defect rate depends on the nature of the software. An arcade video game designed to simulate flying an airplane would presumably have a much higher tolerance for defects than software used to control an actual airliner. Although there are close links with SQA testing departments often exist independently, and there may be no SQA areas in some companies.
Defects and failures:
The software faults occur through the following process. A programmer makes an error (mistake), which results in a defect (fault, bug) in the software source code. If this defect is executed, in certain situations the system will produce wrong results, causing a failure.Not all defects will necessarily result in failures. For example, defects in dead code will never result in failures. A defect can turn into a failure when the environment is changed. Examples of these changes in environment include the software being run on a new hardware platform, alterations in source data or interacting with different software.
Input combinations and preconditions:
A problem with software testing is that testing all combinations of inputs and preconditions is not feasible when testing anything other than a simple product.This means that the number of defects in a software product can be very large and defects that occur infrequently are difficult to find in testing. More significantly, parafunctional dimensions of quality--for example, usability, scalability, performance, compatibility, reliability--can be highly subjective; something that constitutes sufficient value to one person may be intolerable to another.
Static vs. dynamic testing:
There are many approaches to software testing. Reviews, walkthroughs or inspections are considered as static testing, whereas actually running the program with a given set of test cases in a given development stage is referred to as dynamic testing.
Software verification and validation:
Software testing is used in association with verification and validation
Verification: Have we built the software right (i.e., does it match the specification)?
Validation: Have we built the right software (i.e., is this what the customer wants)?
The software testing team:
Software testing can be done by software testers. Until the 1950s the term software tester was used generally, but later it was also seen as a separate profession. Regarding the periods and the different goals in software testing there have been established different roles: test lead/manager, test designer, tester, test automater/automation developer, and test administrator.
History:
The separation of debugging from testing was initially introduced by Glenford J. Myers in 1979. Although his attention was on breakage testing, it illustrated the desire of the software engineering community to separate fundamental development activities, such as debugging, from that of verification. Dr. Dave Gelperin and Dr. William C. Hetzel classified in 1988 the phases and goals in software testing in the following stages
Until 1956 - Debugging oriented
1957-1978 - Demonstration oriented
1979-1982 - Destruction oriented
1983-1987 - Evaluation oriented
1988-2000 - Prevention oriented
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