How do you apply shift-left testing?

Direct answer

What a strong answer covers

How it works

Shifting left means finding problems where they are cheapest to fix, which is before code is written and while it is being written. It starts with examples: before a story is built, the team writes concrete scenarios including edge cases and failures, which become both the acceptance criteria and the first tests. Static checks, schema validation, and linters run in the editor and on every commit. Component and contract tests run in the pull request so developers get feedback in minutes. Test engineers pair on design and review rather than receiving builds at the end. Production monitoring stays in place, because shifting left reduces defects, it does not eliminate them.

Example

For a new discount feature, the three amigos session produced twelve scenarios including stacked discounts and expired codes, which the developer turned into unit tests before writing the logic. A schema validator in the editor flagged a malformed API example, and a contract test in the pull request caught that the frontend expected a field the backend had not added. The feature reached the shared environment with no defects found there, and a canary rollout still caught a locale issue in production.

Common mistakes

• Treating shift-left as moving the same manual testing earlier in the calendar.
• Writing scenarios after the code so they mirror the implementation instead of the intent.
• Removing production monitoring because testing now happens earlier.

A useful answer structure

Answer from your own work.

Do not memorise a script: use only examples you can explain honestly in follow-up questions.