jest.config.js

export default {

    // ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

    // Only run coverage for the TypeScript files in lib as everything in the root of `./src`
    //    is an entry point or constants
    collectCoverageFrom: [
        'src/lib/**/*.ts',
    ],

    // ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

    // Enable useESM true for ts-jest config
    transform: {

        // Use ts-jest transform with ESM module support
        // - Regex supports ts to use ts-jest with useESM flag
        // - https://kulshekhar.github.io/ts-jest/docs/next/guides/esm-support
        '^.+\\.ts$': [
            'ts-jest',
            { useESM : true },
        ],
    },

    // Treat all TypeScript files as ESM modules
    // - .js not included on this list due to being automatically included based off of the `package.json`
    //   `"type" : "module"` definition (will throw error if you add .js to this!)
    extensionsToTreatAsEsm : [ '.ts' ],

    // Remove the .js extension when running tests because Jest is directly running the TypeScript
    //    files instead of compiling them to JavaScript
    moduleNameMapper: {

        // Remove the .js extension when running tests because Jest is directly running the TypeScript
        //    files instead of compiling them to JavaScript
        '^(\\.{1,2}/.*)\\.js$': '$1',

        // Map the @src path alias defined in `tsconfig.json`
        '^@src/(.*)' : '<rootDir>/src/$1',
    },
};