Small example of how code coverage highlights insufficient unit testing and shows exactly which parts of your code need to be refactored.
The repo was created with Node.js version 10.15.1, the latest LTS version should be sufficient. Just run npm install to prepare the project. The code provided here is not intended to do anything, it is just an example, so run the test and code coverage using
npm run coverageThe coverage results are output to the coverage folder and you can see the html summary report at coverage/lcov-report/index.html which should open locally in your browser. Note, the coverage folder is not part of this repo - it will be created when you run npm run coverage.
The code example is contrived and not something that would pass a code review! However the code looks reasonable at first glance (if you squint).
The test results look sensible enough
If we pull in the coverage report too, we immediately see there is a problem
Open the coverage report, found at coverage/lcov-report/index.html, in your browser - a double-click should do it - and look at the coverage report on the code itself t_he problems stick out like a sore thumb!
Now we know exactly where the tests and the code are not up to standard - time to refactor and get our gold-plated 100% coverage.