Shift-left testing: Difference between revisions

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'''Shift -left testing''' <ref>{{cite web|url=http://blog.sei.cmu.edu/post.cfm/four-types-shift-left-testing-082 |title=Four Types of Shift Left Testing |author=Donald Firesmith | date=23 March 2015 |accessdate=27 March 2015}}</ref> is an approach to [[software testing]] and [[system testing]] in which testing is performed earlier in the lifecycle (i.e., moved left on the project timeline). It is the first half of the maxim "Test early and often."<ref>{{cite web|url=https://msdn.microsoft.com/en-us/library/vstudio/ee330950%28v=vs.110%29.aspx |title=Test Early and Often |author=Microsoft | date=2012 |accessdate=27 March 2015}}</ref>

== Harm due to late testing ==

Shift -left testing is important because it helps to prevent the following types of harm due to late testing:

* Testers may be less involved in initial planning, often resulting in insufficient resources being allocated to testing.

* Many requirements, architecture, and design defects are not uncovered and fixed until after significant effort has been wasted on their implementation.

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* There is less time to fix defects found by testing, thereby increasing the likelihood that they will be postponed until later increments or versions of the system, which creates a “bow wave” of [[technical debt]] that can sink projects if it grows too large.

== Types of shift -left testing ==

There are four basic ways to shift testing earlier in the life-cycle (that is, leftward on the classic [[V-model]]). These can be referred to as traditional shift -left testing,<ref>{{cite web|url=http://www.velocitypartners.net/blog/2014/01/28/agile-testing-the-agile-test-automation-pyramid/ |title=Agile Testing - The Agile Test Automation Pyramid |author=Velocity Partners | date=28 January 2014 |accessdate=27 March 2015}}</ref> incremental shift -left testing, Agile/DevOps shift -left testing,<ref>{{cite web|url=http://www.slideshare.net/Urbancode/shift-left |title=Shift Left: Approaches and Practices |author=Paul Bahrs | date=6 November 2014 |accessdate=27 March 2015}}</ref><ref>{{cite web|url=https://www.ibm.com/developerworks/community/blogs/invisiblethread/entry/enabling_devops_success_with_shift_left_continuous_testing?lang=en |title=Enabling DevOps Success with Shift Left Continuous Testing |author=Dibbe Edwards | date=18 September 2014 |accessdate=27 March 2015}}</ref> and model-based shift -left testing.<ref>{{cite web|url=http://blog.sei.cmu.edu/post.cfm/using-v-models-testing-315 |title=Using V Models for Testing |author=Donald Firesmith | date=11 November 2013 |accessdate=27 March 2015}}</ref>

=== Traditional shift -left testing ===

As illustrated in the following figure, traditional shift -left moves the emphasis of testing lower down (and therefore slightly to the left) on the right hand side of the classic V model. Instead of emphasizing acceptance and system level testing (e.g., [[GUI testing]] with record and playback tools<ref>{{cite web|url=https://msdn.microsoft.com/en-us/library/dd286714.aspx |title=Record and Playback Manual Tests |author=Microsoft | date= 2013 |accessdate=27 March 2015}}</ref>), traditional shift -left concentrates on [[unit testing]] and [[integration testing]] (e.g., using [[API testing]] and modern test tools). The transition to traditional shift -left testing has largely been completed.{{By whom|date=April 2016}}

<gallery>

Traditional-Shift-Left.jpg|Traditional Shiftshift-left Left Testingtesting

</gallery>

=== Incremental shift -left testing ===

As illustrated in the following figure, many projects developing large and complex software-reliant systems decompose development into a small number of increments (Vs) having correspondingly shorter durations. The shift -left illustrated by the dashed red arrows occurs because parts of the single, large waterfall V model’s types of testing (shown in gray) are shifted left to become increments of the corresponding types of testing in the smaller incremental V models. When each increment is also a delivery to the customer and operations, then incremental shift -left testing shifts both developmental testing and operational testing to the left. Incremental shift -left testing is popular when developing large, complex systems, especially those incorporating significant amounts of hardware. Like traditional shift -left, the transition to incremental shift -left has also been largely completed.

<gallery>

Incremental-Shift-Left.jpg|Incremental Shiftshift-left Left Testingresting

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=== Agile/DevOps shift -left testing ===

As illustrated in the following figure, [[Agile software development|Agile]] and [[DevOps]] projects have numerous short duration Vs (a.k.a., sprints) in lieu of a single or small number of V as in the previous two examples of shift -left testing. These small Vs would also be modified if one or more early sprints are used to block out the basic requirements and architecture or if test-first and [[test-driven development]] (TDD) are being performed. The shift -left occurs because the types of testing on the right sides of the earliest of these tiny Vs are to the left of the corresponding types of testing on right side of the larger V(s) they replace. While the following figure appears remarkably the same for Agile and DevOps, Agile testing is typically restricted to developmental testing and does not include operational testing, which occurs once the system is placed into operation. The transition to Agile/DevOps shift -left testing is currently popular and ongoing.

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Agile_DevOps_Shift_Left_Testing.jpg|Agile/DevOps Shiftshift-left Left Testingtesting

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=== Model-based shift -left testing ===

The previous forms of shifting testing left all concentrated on beginning the testing of software earlier in the development cycle. Waiting until software exists to begin testing, however, largely and unnecessarily limits the use of testing to uncovering coding defects. This delay is particularly disturbing because from 45 percent to 65 percent of defects are introduced in the requirements, architecture, and design activities.<ref>{{cite web|url=http://www.iiste.org/Journals/index.php/CEIS/article/viewFile/3533/3581 |title=Quality Flaws: Issues and Challenges in Software Development |author1=P Mohan |author2=A Udaya Shankar |author3=K JayaSriDevi |last-author-amp=yes | date=2012 |accessdate=27 March 2015}}</ref>

As illustrated in the following figure, model testing moves testing to the left side of the Vs by testing executable requirements, architecture, and design models. This shift enables testing to begin almost immediately, instead of waiting a long time (traditional), medium time (incremental), or a short time (Agile/DevOps) until software on the right side of the Vs is available to test. This trend is just beginning.

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Model-Shift-Left.jpg|Model-Basedbased Shiftshift-left Left Testingtesting

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