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1、Agile Testing StrategiesScott AmblerAs Scott shows here, the quality of your system is only as good as the quality of your testing efforts.Scott is a DDJ Senior Contributing Editor and author of numerous IT books. He can be contacted at scottAmbler.html. 1 Philosophical GroundworkOver the past few
2、months, Ive had more and more people ask me about how we go about testing on agile projects. Agile developers are definitely test infected, and this month, I explore several strategies for testing on agile software development projects. A word of warning: Although we clearly dont follow our fathers
3、serial testing methodology of yesteryear, I suspect that we can still learn a few tricks from dear old dad.Lets start by setting the philosophical groundwork: First, you want to test as early as you possibly can because the potential impact of a defect rises exponentially over time (this isnt always
4、 true, but its something to be concerned about). In fact, many agile developers prefer a test-first approach. Second, you want to test as often as possible, and more importantly, as effectively as possible, to increase the chance that youll find defects. Although this increases your costs in the sho
5、rt term, studies have shown that greater investment in testing reduces the total cost of ownership of a system due to improved quality. Third, you want to do just enough testing for your situation: Commercial banking software requires a greater investment in testing than membership administration so
6、ftware for your local Girl Scouts group. Fourth, pair testing, just like pair programming and modeling with others, is an exceptionally good idea. My general philosophy is that software development is a lot like swimmingits very dangerous to do it alone.2. Testing Throughout the LifecycleFigure 1 pr
7、esents a high-level view of the agile lifecycle for the purpose of testing (see Initiating an Agile Project at for details). Agile projects go through an often short Initiation phase (Iteration 0) where we set the foundation for the project; a Construction phase where we develop the system in an ev
8、olutionary (iterative and incremental) manner; an End Game phase where we transition our system into production; and a Production phase where we operate the system and support users. Dont fear the serial boogeyman: The Initiation phase is not a requirements phase, nor is the End Game a testing phase
9、. Click image to view at full sizeFigure 1: Test activities during the agile lifecycle. Testing activities vary throughout the lifecycle. During Iteration 0, you perform initial setup tasks. This includes identifying the people who will be on the external investigative testing team, identifying and
10、potentially installing your testing tools, and starting to schedule scarce resources such as a usability-testing lab if required. If your project has a deadline, you likely want to identify the date into which your project must enter the End Game. The good news is that youll discover that increased
11、testing during construction iterations enables you to do less testing during the End Game.A significant amount of testing occurs during construction iterationsremember, agilists test often, test early, and usually test first. This is confirmatory testing against the stakeholders current intent and i
12、s typically milestone-based at the unit level. This is a great start, but its not the entire testing picture (which is why we also need investigative testing that is risk-based at more of an integration level). Regardless of the style, your true goal should be to test, not to plan to test, and certa
13、inly not to write comprehensive documentation about how you intend to hopefully test at some point. Agilists still do planning, and we still write documentation, but our focus is on high-value activities such as actual testing.During the End Game, you may be required to perform final testing efforts
14、 for the release, including full system and acceptance testing. This is true if you are legislated to do so (common in life-critical situations such as medical software development) or if your organization has defined service-level agreements with customers who require it. Luckily, if youve tested e
15、ffectively during the construction iterations, your final testing efforts will prove to be straightforward and quick. If youre counting on doing any form of serious testing during the End Game, then youre likely in trouble because your team wont have sufficient time to act on any defects that you do
16、 find.3. Testing During a Construction IterationThe majority of testing occurs during construction iterations on agile projects. Your testing effort, just like your system, evolves throughout construction. Figure 2 depicts two construction iterations, indicating that there is confirmatory testing performed by the team, and in parallel, investigative testing
