Chrysler brought in Kent Beck ,  a prominent Smalltalk practitioner, to do performance tuning on the system, but his role expanded as he noted several problems with the development process. He took this opportunity to propose and implement some changes in development practices - based on his work with his frequent collaborator, Ward Cunningham.
Beck describes the early conception of the methods: . The first time I was asked to lead a team, I asked them to do a little bit of the things I thought were sensible, like testing and reviews. The second time there was a lot more on the line. I thought, "Damn the torpedoes, at least this will make a good article," [and] asked the team to crank up all the knobs to 10 on the things I thought were essential and leave out everything else. Beck invited Ron Jeffries to the project to help develop and refine these methods.
Jeffries thereafter acted as a coach to instill the practices as habits in the C3 team. Information about the principles and practices behind XP disseminated to the wider world through discussions on the original wiki , Cunningham's WikiWikiWeb. Various contributors discussed and expanded upon the ideas, and some spin-off methodologies resulted see agile software development.
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Also, XP concepts have been explained [ by whom? Authors in the series went through various aspects attending XP and its practices. The series included a book critical of the practices. XP generated significant interest among software communities in the late s and early s, seeing adoption in a number of environments radically different from its origins. The high discipline required by the original practices often went by the wayside, causing some of these practices, such as those thought too rigid, to be deprecated or reduced, or even left unfinished, on individual sites.
For example, the practice of end-of-day integration tests for a particular project could be changed to an end-of-week schedule, or simply reduced to testing on mutually agreed dates. Such a more relaxed schedule could avoid people feeling rushed to generate artificial stubs just to pass the end-of-day testing. A less-rigid schedule allows, instead, the development of complex features over a period of several days. Meanwhile, other agile-development practices have not stood still, and as of [update] XP continues to evolve, assimilating more lessons from experiences in the field, to use other practices.
In the second edition of Extreme Programming Explained November , five years after the first edition, Beck added more values and practices and differentiated between primary and corollary practices. The Theory of Sustainable Software Development explains why extreme programming teams can thrive in spite of team disruptions. Extreme Programming Explained describes extreme programming as a software-development discipline that organizes people to produce higher-quality software more productively. XP attempts to reduce the cost of changes in requirements by having multiple short development cycles, rather than a long one.
In this doctrine, changes are a natural, inescapable and desirable aspect of software-development projects, and should be planned for, instead of attempting to define a stable set of requirements. Extreme programming also introduces a number of basic values, principles and practices on top of the agile programming framework. XP describes four basic activities that are performed within the software development process: coding, testing, listening, and designing. Each of those activities is described below. The advocates of XP argue that the only truly important product of the system development process is code — software instructions that a computer can interpret.
Without code, there is no working product. Coding can be used to figure out the most suitable solution. Coding can also help to communicate thoughts about programming problems. A programmer dealing with a complex programming problem, or finding it hard to explain the solution to fellow programmers, might code it in a simplified manner and use the code to demonstrate what he or she means. Code, say the proponents of this position, is always clear and concise and cannot be interpreted in more than one way. Other programmers can give feedback on this code by also coding their thoughts.
Testing is central to extreme programming. System-wide integration testing was encouraged, initially, as a daily end-of-day activity, for early detection of incompatible interfaces, to reconnect before the separate sections diverged widely from coherent functionality. However, system-wide integration testing has been reduced, to weekly, or less often, depending on the stability of the overall interfaces in the system.
Programmers must listen to what the customers need the system to do, what " business logic " is needed. They must understand these needs well enough to give the customer feedback about the technical aspects of how the problem might be solved, or cannot be solved. Communication between the customer and programmer is further addressed in the planning game.
From the point of view of simplicity, of course one could say that system development doesn't need more than coding, testing and listening.
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If those activities are performed well, the result should always be a system that works. In practice, this will not work. One can come a long way without designing but at a given time one will get stuck. The system becomes too complex and the dependencies within the system cease to be clear. One can avoid this by creating a design structure that organizes the logic in the system. Good design will avoid lots of dependencies within a system; this means that changing one part of the system will not affect other parts of the system. Extreme programming initially recognized four values in communication, simplicity, feedback, and courage.
A new value, respect, was added in the second edition of Extreme Programming Explained. Those five values are described below.
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Building software systems requires communicating system requirements to the developers of the system. In formal software development methodologies, this task is accomplished through documentation. Extreme programming techniques can be viewed as methods for rapidly building and disseminating institutional knowledge among members of a development team.
The variant types of activities, carried out during extreme programming development phase, may be seen as under:. Code is the set of instructions, which is execute, to carry out a specific task. It is the smallest and basic working feature of a software application, which derives the development of complete software product. A code should adhere to standards and available specifications. The programmers generate the code, and subsequently produces the programs. The testing activity involves, verifying and validating the functionality of the code, which is carried out by the programmer, itself.
Basically, a programmer makes use of automation, to execute the automated unit tests. Acceptance testing , is a common seen testing technique, in the extreme programming. It empowers, to reduce the complexity of the process, and subsequently avoids the situation of dependencies, in the system. The above said activities may be implemented, by making use of several and best available practices, in the field of software engineering. However, there are 12 significant practices, specified for the purpose of implementing the XP's activities, and is listed below: Software product, on which testing needs to be performed.
Pair Programming: Involves two programmers, working on the same system, to generate programming codes.
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Planning game: It may be seen as a planning phase or activity of the XP, done for each iteration, and involves meetings, which may be held, once in a week. Test-Driven Development: Development process, driven by the failures of the tests, so as to design and create new code and functionality, accordingly. Whole Team: Here, whole team consists of, not only the team member, but the client and stakeholders, along with the targeted customers, which are responsible for driving the development process.
Continuous Integration: Saving various versions of a software product, and delivering updated and current version, thereby avoiding delays in the projects. Refactoring: Constantly, applying and implementing changes, to enhance the quality of the code. It would be a mistake, though, to conclude that this is the main way a tester benefits the team.
In fact, putting too much emphasis on this aspect can lead to a dysfunctional team, where responsibility for testing and quality are placed solely on the tester.
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Sure, the tester is focused on the testing and finding defects and quality. But so is everyone else on the team. For instance, one hallmark of XP is the "test-first" pattern, in which programmer pairs write the unit tests first, before they write one line of code.
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