Shift Left Testing means moving testing earlier in the development process, so defects are found
sooner and fixes are cheaper.
Unit testing as part of CI is 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.
