Test a create-react-app index.js file

If 100% coverage on your project is your goal and the code in your index.js file is trivial, then it might be a good option to exclude the file from the coverage report, as Andreas Köberle points out in his answer.

Create-react-app currently only supports these four keys in the Jest configuration (source):

collectCoverageFrom
coverageReporters
coverageThreshold
snapshotSerializers

This is why

coveragePathIgnorePatterns": ["src/index.js"]

won’t work.

Add following code to the most outer scope of your package.json file:

"jest": {
  "collectCoverageFrom": [
    "src/**/*.{js,jsx}",
    "!src/index.js"
  ]
}

In the image below you see the output of a test run with this code added to the package.json of the initial app created with create-react-app v1.4.3. Note that the index.js file doesn’t show up in the report anymore and also doesn’t affect the coverage percentage.