Note for Software Testing - ST By Amity Kumar

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UNIT I TESTING BASICS 1.1 Testing as an engineering activity This is an exciting time to be a software developer. Software systems are becoming more challenging to build. They are playing an increasingly important role in society. People with software development skills are in demand. New methods, techniques, and tools are becoming available to support development and maintenance tasks. Because software now has such an important role in our lives both economically and socially, there is pressure for software professionals to focus on quality issues. Poor quality software that can cause loss of life or property is no longer acceptable to society. Failures can result in catastrophic losses. Conditions demand software development staffs with interest and training in the areas of software product and process quality. Highly qualified staff ensure that software products are built on time, within budget, and are of the highest quality with respect to attributes such as reliability, correctness, usability, and the ability to meet all user requirements. Using an engineering approach to software development implies that: the development process is well understood; projects are planned; life cycle models are defined and adhered to; standards are in place for product and process; measurements are employed to evaluate product and process quality; components are reused; validation and verification processes play a key role in quality determination; engineers have proper education, training, and certification. 1.2 Role of process in software quality The need for software products of high quality has pressured those in the profession to identify and quantify quality factors such as usability, testability, maintainability, and reliability, and to identify engineering practices that support the production of quality products having these favorable attributes. Among the practices identified that contribute to the development of highquality software are project planning, requirements management, development of formal specifications, structured design with use of information hiding and encapsulation, design and code reuse,inspections and reviews, product and process measures, education and training of software professionals, development and application of CASE tools, use of effective testing techniques, and integration of testing activities into the entire life cycle. In addition to identifying these individual best technical and managerial practices, software researchers realized that it was important to integrate them within the context of a high-quality software development process. Process, in the software engineering domain, is the set of methods, practices, standards, documents, activities, policies, and procedures that software engineers use to develop and maintain a software system and its associated artifacts, such as project and test plans, design documents, code, and manuals. 1

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It also was clear that adding individual practices to an existing software development process in an ad hoc way was not satisfactory. The software development process, like most engineering artifacts, must be engineered. That is, it must be designed, implemented, evaluated, and maintained. As in other engineering disciplines, a software development process must evolve in a consistent and predictable manner, and the best technical and managerial practices must be integrated in a systematic way. These models allow an organization to evaluate its current software process and to capture an understanding of its state. Strong support for incremental process improvement is provided by the models, consistent with historical process evolution and the application of quality principles. The models have received much attention from industry, and resources have been invested in process improvement efforts with many successes recorded. All the software process improvement models that have had wide acceptance in industry are high-level models, in the sense that they focus on the software process as a whole and do not offer adequate support to evaluate and improve specific software development sub processes such as design and testing. Most software engineers would agree that testing is a vital component of a quality software process, and is one of the most challenging and costly activities carried out during software development and maintenance. 2

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1.3 Testing as a process The software development process has been described as a series of phases, procedures, and steps that result in the production of a software product. Embedded within the software development process are several other processes including testing. Some of these are shown in Figure 1.3. Testing itself is related to two other processes called verification and validation as shown in Figure 1.3. Validation is the process of evaluating a software system or component during, or at the end of, the development cycle in order to determine whether it satisfies specified requirements. Validation is usually associated with traditional execution-based testing, that is, exercising the code with test cases. Verification is the process of evaluating a software system or component to determine whether the products of a given development phase satisfy the conditions imposed at the start of that phase [11]. Verification is usually associated with activities such as inspections and reviews of software deliverables. Testing itself has been defined in several ways. Two definitions are shown below. Testing is generally described as a group of procedures carried out to evaluate some aspect of a piece of software. 3

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Testing can be described as a process used for revealing defects in software, and for establishing that the software has attained a specified degree of quality with respect to selected attributes. Note that these definitions of testing are general in nature. They cover both validation and verification activities, and include in the testing domain all of the following: technical reviews, test planning, test tracking, test case design, unit test, integration test, system test, acceptance test, and usability test. The definitions also describe testing as a dual-purpose process—one that reveals defects, as well as one that is used to evaluate quality attributes of the software such as reliability, security, usability, and correctness. Also note that testing and debugging, or fault localization, are two very different activities. The debugging process begins after testing has been carried out and the tester has noted that the software is not behaving as specified. Debugging, or fault localization is the process of (1) locating the fault or defect, repairing the code, and (3) retesting the code. (2) Testing as a process has economic, technical and managerial aspects. Economic aspects are related to the reality that resources and time are available to the testing group on a limited basis. In fact, complete testing is in many cases not practical because of these economic constraints. An organization must structure its testing process so that it can deliver software on time and within budget, and also satisfy the client‘s requirements. The technical aspects of testing relate to the techniques, methods, measurements, and tools used to insure that the software under test is as defect-free and reliable as possible for the conditions and constraints under which it must operate. Testing is a process, and as a process it must managed. Minimally that means that an organizational policy for testing must be defined and documented. Testing procedures and steps must be defined and documented. Testing must be planned, testers should be trained, the process should have associated quantifiable goals that can be measured and monitored. Testing as a process should be able to evolve to a level where there are mechanisms in place for making continuous improvements. 1.4 Basic definitions Errors An error is a mistake, misconception, or misunderstanding on the part of a software developer. In the category of developer we include software engineers, programmers, analysts, and testers. For example, a developer may misunderstand a design notation, or a programmer might type a variable name incorrectly. Faults (Defects) A fault (defect) is introduced into the software as the result of an error. It is an anomaly in the software that may cause it to behave incorrectly, and not according to its specification. 4