Solving ESLint Jest warnings

I recently started adding Test coverage to a react-native project and one our determination as a team is to have zero ESLint warnings throughout the code-base.

The issue with Jest is that it's built-in functions such as it and expect are implicitly defined in the global js context of the test file, so at runtime the test suite works correctly but ESLint reports such functions as undefined functions.

The solution is to enable the jest plugin for eslint:

yarn add eslint-plugin-jest

Then in your .eslintrc.json enable jest globals:

"env": {
  "jest/globals": true

That's pretty much it.