Software testing is considered to be the most important part of the software life cycle from design to implementation and maintenance of a software project. Testing is a process of exercising a program with a specific intent of finding errors prior to delivery to the end user. It occurs at every phase of system construction. The different levels of testing reveal that it is not the only phase of the software life cycle; it is a set of activities performed throughout the software life cycle.

Software testing may be perceived as a subfield of Software Quality Assurance but it typically exists independently. 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 are in the code. A common practice of software testing is that it is accomplished by an independent group of testers after finishing the software product and before it is shipped to the customer which is being used as a project buffer to compensate for the project delays. Normally, people assume that all the activities as illustrated in Figure 1 are only testing; but the activities after implementation are only considered as testing.

It is essential to review the definition of software testing in the literature. According to Wikipedia, "Software testing is a process used to identify the correctness, completeness and quality of developed computer software". Actually, testing can never establish the correctness of computer software, as this can only be done by formal verification (and only when there is no mistake in the formal verification process). It can only find defects, not prove that there are none.

As EW Dijkstra states, testing can establish the presence of errors but cannot guarantee their absence. The process of implementing or evaluating a system or a system component by manual or automated means is to verify that it fits certain requirements or to specify the differences between expected and actual results. These tests are conducted mainly to evaluate response time, memory usage, throughput, device utilization, and execution time.