Test pyramid and risk-based coverage

The test pyramid is a feedback heuristic, not a quota: many fast unit checks at the base, fewer integration tests across real boundaries, and a thin cap of E2E flows for business-critical journeys. Risk-based coverage means you invest where failure is expensive—payments, auth, data loss—not where code is merely voluminous.

					        / E2E \
       /-------\
      / Integr. \
     /-----------\
    /    Unit     \
				

Balance speed with confidence: units give pinpoint failures; integration catches wiring mistakes; E2E proves the product works for users.

On interviews: explain why an inverted pyramid (many slow UI tests) creates flaky CI and slow feedback, and how you would reprioritize by risk.

Common pitfalls: treating pyramid ratios as law, skipping integration because units pass, or running full E2E for every edge case.

The trade-off is faster feedback versus broader confidence—more E2E increases certainty but multiplies maintenance and flake.

Checklist:

• Name the three layers and what each catches.
• Tie coverage to business risk, not line coverage alone.
• Describe how you would shrink a bloated E2E suite.