How the __tests__ directories can be ignored while running yarn build in production mode.

export default {
  // ...
  ignore: [
    '**/_tests_/**'
  ],
  // ...
}

export default {
  // ...
  ignore: [
    '**/_tests_/**'
  ],
  // ...
}

  build: {
    extend(config, { isClient, isServer }) {
      if (isClient || isServer) {
        // Exclude _tests_ directories from being bundled into your production build
        config.module.rules.push({
          test: /_tests_/, 
          loader: 'null-loader'
        });
      }
    }
  },

  build: {
    extend(config, { isClient, isServer }) {
      if (isClient || isServer) {
        // Exclude _tests_ directories from being bundled into your production build
        config.module.rules.push({
          test: /_tests_/, 
          loader: 'null-loader'
        });
      }
    }
  },