How to: ![✔] 4.7 Check your test coverage, it helps to identify wrong test patterns
**TL;DR:** Code coverage tools like [Istanbul](https://github.com/istanbuljs/istanbuljs)/[NYC](https://github.com/istanbuljs/nyc) are great for 3 reasons: it comes for free (no effort is required to benefit this reports), it helps to identify a decrease in testing coverage, and last but not least it highlights testing mismatches: by looking at colored code coverage reports you may notice, for example, code areas that are never tested like catch clauses (meaning that tests only invoke the happy paths and not how the app behaves on errors). Set it to fail builds if the coverage falls under a certain threshold

**Otherwise:** There won't be any automated metric telling you when a large portion of your code is not covered by testing