Track defect escape rate — how many bugs reach production vs how many you catch in testing. This single metric tells you more about test effectiveness than coverage percentages ever will.
Strong answers go beyond line coverage: defect escape rate (bugs found in production vs testing), defect detection percentage, mean time to detect, test execution time trends, flake rate, test maintenance cost, and coverage of critical user journeys. Best candidates discuss how they use these metrics to improve the testing process, not just report on it.
Tests analytical approach to quality. Candidates who only track pass/fail counts and code coverage are missing the bigger picture. Those who measure testing ROI and use metrics to improve their process demonstrate strategic thinking.