Shift Left Testingmeans moving testing earlier in the development process, so defects are found sooner and fixes are cheaper.
Unit testing as part of CIis the classic "shift left" strategy: automated unit tests run with every code change, catching errors before code moves further down the pipeline.
* Testing in production(A) is "shift right."
* Manual testing(B) is typically late-stage and not automated.
* Biannual vulnerability assessments(D) are after-the-fact and far from "shift left." Extract-style reference:
"Shift left means performing testing activities earlier, for example by including unit tests in the CI process, reducing costly late-stage defects."
-DevOps Handbook
PeopleCert Foundation: "Shift left" is a key DevOps testing principle-find issues fast, fix fast, deploy safely.