What is test coverage and how do you measure it?

Short answer: Test coverage shows how much of your code is tested (lines, branches, functions). Tools to measure: Istanbul/nyc: Most popular coverage tool. Jest: Has built-in coverage reports. Run coverage with nyc: nyc mocha It outputs stats like: % of lines covered % of functions covered % of branches covered Security in Node.js

Real-world example (ShopNest)

A ShopNest BFF in Node.js aggregates catalog and price APIs for the React storefront.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.