@automattic/calypso-jest

This package provides a Jest preset used to run tests in Calypso. In your jest.config.js set the following:

module.exports = {
    preset: '@automattic/calypso-jest',
};

Major features:

Find tests under <rootDir> inside test folder. Valid extensions are .ts, .js, .tsx, .jsx
Can use calypso:src from package.json to resolve a package
Can use conditional exports

Assets transformer

Jest would fail when trying to import asset files that it cannot parse, i.e. they're not plain JavaScript:

const MyFlag = ( { countryCode } ) => (
    <img alt="" src={ require( `flags/${ countryCode }.svg` ).default } />
);

This packages includes a transfomer that be used to transform all those imports to a module that returns the asset file's basename as a string:

const config = {
    transform: {
        '\\.(gif|jpg|jpeg|png|svg|scss|sass|css)$': require.resolve(
            '@automattic/calypso-jest/asset-transform.js'
        ),
    },
};