Where does Performance Testing fit in Agile SDLC?

Is agile software development lifecycle (SDLC) all about sprinting i.e. moving stories from product backlog to sprint backlog and then executing iterative cycles of development and testing? IMHO, not really! We all know that certain changes in an application can be complex, critical or have a larger impact and therefore require more planning before they are included in development iterations. Agile methodologies (particularly Scrum) accommodate for application planning and long-term complex changes to the application in a release planning sprint called Sprint 0 (zero), which primarily driven by business stakeholders, application owners, architects, UX designers, performance testers, etc.


Sprint 0 brings a bit of waterfall process in the agile processes, with two major differences – sprint 0 is shorter in duration (2-4 weeks) and the stress on documentation is not as much as in the waterfall method. In my experience, sprint 0 is more efficient when it is overlapping, so while the development team and testers are working on sprints of the current release; stakeholders, architects, application owners, business analysts, leads (development, QA, performance testing, user interface design), and other personas get together to scope, discuss and design their next release. Sprint 0 is executed like any other sprint, which has contributors (pigs) and stakeholders (chickens) and they meet daily to discuss their progress and blockages. Moreover, sprint 0 need not be as long as the development iteration.


I have seen organizations further divide sprint 0 into two sprints i.e. sprint -1 (minus one) and sprint 0. Sprint -1 is a discovery sprint, to go over user stories to be included in the release and discover potential problems/challenges in the application, processes, infrastructure, etc. The output of sprint -1 results in an updated release backlog, updated acceptance criteria for more clarity, high-level architectural designs, high-level component designs, user interface storyboards and high-level process layouts. Sprint 0 then becomes the design sprint that goes a level deeper to further update the release backlog and acceptance criteria, and delivers user interface wireframes, detailed architectural & component designs, and updated process flows.


The big question is, where does performance testing requirement fit in an agile SDLC described above? While “good” application performance is an expected outcome of any release, its foundation is really laid out during the release planning stage i.e. in sprints -1 and 0. We know that user stories that describe the performance requirements of an application can impact various decisions taken on the application vis-à-vis its design and/or on its implementation. In addition, functional user stories that can potentially affect the performance of an application are also looked at in detail during the release planning stage. Questions like these are asked and hopefully addressed – whether or not the application architecture needs to be modified to meet the performance guidelines; whether or not the IT infrastructure of the testing and production sites are to be upgraded; whether or not newer technologies such as AJAX that are being introduced in the planned release can degrade the performance of the application; whether or not user interface designs that are being applied in the planned release can degrade the performance of the application; whether or not making the application available to new geographies can impact the performance of the application; whether or not expected increase in application usage going to impact its performance; etc. At the end of the sprint -1, the team may choose to drop or modify some performance related stories or take a performance debt on the application.


Going into Sprint 0, the team will have an updated release backlog and acceptance criteria for the accepted user stories. During this sprint, the team weighs application’s performance requirements against the functional and other non-functional requirements to further update the release backlog. At the end of sprint 0, some requirements (functional and non-functional) are either dropped or modified, and detailed designs are delivered for the rest of the stories. Sprint 0 user stories then transition into the sprint planning session for sprints 1-N of the development and testing phase. Throughout these 1-N sprints, the application is tested for functionality, performance and other non-functional requirements so that at the end of every sprint, completed stories can be potentially released.


Agile methodologies also allow for a hardening sprint at the end of sprints 1-N, for an end-to-end functional, integration, security and performance testing. The hardening sprint need not be as long as development sprints (2-4 weeks) and is an optional step in an agile SDLC. This is the last stage where performance testers can catch any issues vis-à-vis performance, before the applications gets deployed to production. But we all know that performance issues found at this stage are more expensive to fix and can have bigger business implications (delayed releases, dissatisfied end-users, delayed revenue, etc.) If the planning in sprint -1 and sprint 0 and subsequent execution in sprint 1-N were done the right way, chances are that the hardening sprint is more of a final feel-good step before releasing the application.

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