The previous forms of shifting testing left all concentrated on beginning the testing of software earlier in the development cycle. WaitinguntilHowever, softwarethey existsall totest begin''after'' testing,software however, largelyexists and unnecessarilyseek limitsto theuncover useonly of testing to uncovering codingimplementation defects. ThisdelayModel istesting particularlytheory disturbingargues because fromthat 45 percent% to 65 percent% of defects are introduced inbefore theimplementation, during requirements gathering, 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, modelModel-based testing moves testing to the left side of the Vs, by testing executable requirements, architecture, and design models. This shift enablesbegins testing to begin almost immediately, instead of waiting a long time (traditional testing), medium time (incremental testing), or a short time (Agile/DevOps) untilfor software onto become available to the right side of the Vs. is available to test. This trend is just beginning.
