jest.config.js

module.exports = {
  // An array of file extensions your modules use
  moduleFileExtensions: ['js', 'jsx', 'ts', 'tsx', 'json'],
  // A list of paths to directories that Jest should use to search for files in.
  roots: ['<rootDir>/src'],
  /*
    The glob patterns Jest uses to detect test files.
    We're looking for all .ts and .js extensions
    (including x variants) as well as files with .spec and .test suffixes
  */
  testMatch: [
    '**/__tests__/**/*.+(ts|tsx|js|jsx)',
    '**/?(*.)+(spec|test).+(ts|tsx|js|jsx)',
  ],
  /*
    A map from regular expressions to paths to transformers.
    A transformer is a module that provides a synchronous function
    for transforming source files.

    For example, if you wanted to be able to use a new language feature
    in your modules or tests that aren't yet supported by node,
    you might plug in one of many compilers that compile a future version
    of JavaScript to a current one. Examples: Babel, Typescript, etc.
  */
  transform: {
    // Jest doesn't handle non JavaScript assets by default.
    '.+\\.(css|styl|less|sass|scss|png|jpg|jpeg|ttf|woff|woff2)$':
      /*
        You can use this module to avoid errors when
        importing non JavaScript assets.
      */
      'jest-transform-stub',
    /*
      If you have JavaScript files that are transformed by Babel,
      you can enable support for Babel by installing the babel-jest plugin.
      Non-Babel JavaScript transformations can be handled with
      Jest's transform config option.

      Note: if you are using babel-jest with additional code preprocessors
      (and we are because we're using ts-jest for TypeScript files),
      you have to explicitly define babel-jest as a transformer for your
      JavaScript code to map .js files to the babel-jest module.
    */
    '^.+\\.(js|jsx)?$': 'babel-jest',
    /*
      A TypeScript preprocessor with source map support for Jest
      that lets you use Jest to test projects written in TypeScript.
    */
    '^.+\\.(ts|tsx)?$': 'ts-jest',
  },
  // ignore dependency folder for tests
  transformIgnorePatterns: ['<rootDir>/node_modules/'],
};